let's try to not project modern laws and practices concerning weapons onto a medieval fantasy game.
I just used that as an example - people carry personal weapons because they can't rely on law enforcement to be everywhere to protect them from physical danger. Or they're a bit out there and have a stockpile of foil to line their hat with.
In medieval times peasants usually were the military and they were, rather than allowed to, required to arm themselves so that their lord could levy an army from among the peasants when needed. A DF style standing military would be either an extremely expensive mercenary force or a very limited group of a lords retainers, probably nobles themselves.
Which is essentially what we currently treat out militias as - Standing armies made of a small number of professional soldiers, and generally more than sufficient to deal with a given threat if properly armed and equipped, they just physically can't be guaranteed to be able to respond to
every single threat or waste their time escorting every single dwarf who has to go to dangerous territory.
That also ties in nicely to what i said before - an armed populace could very well become a good recruitment ground for the professional defense force, pulling the bravest dwarves who either continually chose to put themselves in danger or show an astonishing degree of adeptness and/or luck in conflicts with wildlife and such. A means of semi-autonomously finding the best-suited beards for line duty.
I know I'm opening a can of worms, but...
Have you considered that the militia and fortress guard can't be everywhere at once? That's like asking why a private arms industry exists in the United States - people arm themselves if they don't feel safe and that local law enforcement or military is unable or unwilling to protect them.
If there is a shortage of military, you would be spending all that metal to make more of them, not arming civilians to exist without them.
A shortage of soldiers can be due to attrition or too much ground to cover. Your militia (which most of us treat as a professional army, let's face it,) can't physically escort everyone with a dangerous job (weavers, fishers, herbalists, and other "outside" work generally,) patrol the whole of the map's countryside, patrol the whole of the caverns, man/patrol the general perimeter of say, an overland keep, and help escort a caravan into the fort all at the same time, not without taking up a huge portion of the population unless you really use them as a militia - that is a part-time military force.
The private arms industry in the United States is basically built on a self-perpetuating anti-social mass-delusion, this is why the thread amounts to essentially asking the devs to add in new mechanics for the player to be stupid. We are not really talking here about making civilian self-defense illegal, but rather not wasting resources on it; it's less a 'if you have a gun you go to prison' than 'yes you can have a gun but good luck getting one'.
I just used that as an example, chill dude. The reason is the same - some dwarves would want them for one reason or another, and this could actually affect them via the emotions/stress system.
Say a vampire gobbled up four dwarves and left many nearly dead - the population should be concerned for their own safety, especially if you haven't found the culprit yet (or perhaps have it come after it hasn't been solved for several seasons.) To them, it means the fortress guard is unwilling or unable to protect them, so they'll take matters into their own hands and arm themselves accordingly.
Others may simply purchase weapons and go to the barracks to watch the troops train of their own volition, their ownership of personal weapons being so that they can join if the need arises, or to protect their fellow dwarves if the militia is unavailable (while slao plainly showing who would make for a good militia recruit if needed.) This could affect different personality types as well - cowardly dwarves will have a slight stress reduction because someone is armed nearby to protect them or at least keep something busy while they run away, while ones who are more on the power hungry or pacifistic might be annoyed or agitated by it.
Urist McParanoid was
concerned about the poor access to private weapons due to unsolved murders/ Urist McParanoid is
Frightened/
Felt safer with armed dwarves nearby.
Urist McMartialMinded was
annoyed by a lack of personal weapons/lack of quality weapons.
Urist McWorried was
reassured of their family's/friends'/ their own safety by having a weapon on hand.
Urist McGoblinInside was
angered by the presence of other armed dwarves/ Urist McGoblinInside was
contented at the fact he was the only armed dwarf in the room.
Urist McHippy felt
annoyed by the armed dwarves near him recently.
Being poorly armed is basically worse than being unarmed, if you are unarmed an armed person has a pretty good probability of ignoring you and pursuing whatever cause it is they are actually interested in, (you are out of luck if your death is what they want) but if you are poorly armed then a better armed person has to engage you in combat but you will probably lose. An armed criminal robs an unarmed person and he can just take what he wants without hurting the victim, but if an armed criminal takes on an armed victim he has no choice but to shoot the victim and take their valuables.
In DF most things tend to want to kill you. A bandit deciding to kill someone because they hesitated to drop their weapon and coin pouch would be entirely reasonable within context, but now that victim being armed and this likely being close combat, now puts the bandit at significant risk of serious injury as well. Plus if they try to mug a dwarf who went to the militia on their own to observe and learn, they might even put up a better fight than expected, or even kill the bandit instead due to the game's semi-random nature in combat (That planter just stabbed you in the leg with his work knife, so now you're fighting with greatly reduced agility on the ground and he's still moving at full capacity, and may try to finish you or run to get help.)
It gets worse. A large group of poorly armed folks can by weight of numbers overpower a smaller number of better armed opponents.
If anything this is actually kind of a point in favor of this, as an armed mob might be able to overpower an enemy invasion, albeit potentially with serious casualties. If anything, this could be a good source of FUN because your bravest citizens opt to form an ad hoc militia to assist your soldiers and follow the milita commander's squad into battle (perhaps complete with a little announcement of this event!
"
Urist McStupidlyBrave has rallied an armed mob to assist the militia, and will follow Militia Commander Urist McMurdersmith until the invaders are driven off!" and I put that in yellow cause this could actually be helpful or a serious issue, depending on your militia's condition.)
This means that an armed populace actively undermines law enforcement,
Dwarves believe in the rule of law generally, so for them it'd be far less of an issue. Plus at present the police for a fortress only ever has at most ten dwarves, and seldom would anyone ever need more than that to enforce the law. Cause really, come on. if you need more than that to keep a lid on things, is your fort even gonna be standing much longer?
an unarmed population means you do not need as many law-enforcers because you do not have to worry so much about a mob of criminals/rebels/dissidents actually being able to ambush and kill the law enforcers. An armed population means you have to maintain a larger military in order to control it, all the while the weapons that the populace have are not available to arm said military. In effect an armed population means that every action carry out by law enforcement has to be essentially a military operation, that is to say it has to actually has to involve the possibility of facing organized armed resistance.
Dwarves as said are unlikely to have this issue due to a general belief in the rule of law, including dwarves sorting out how to handle the sudden loss of primary leadership without force. Power-hungry and generally ill-thinking of the law dwarves appear to head for the hills and turn bandit, which basically gets them marked for death for murder/treason anyway since they'll inevitably end up killing someone. Additionally, perhaps this could give titles a purpose besides showing prowess in general - titled dwarves nearby could greatly reduce the chances anyone is willing to do something uncivil, because that dwarf has killed at least five noteworthy foes, and wouldn't be afraid to add them to that body count - which also encourages us to bloody the fortress guard a bit, because having hardened combat veterans as part of the fortress guard would make them more effective at their job.
And besides that, who said we were gonna give the citizens access to the good shit? Wealthier dwarves or those with a certain amount of respect in the community maybe, but in general most will suffice with knives, sickles, fishing spears, clubs and such, rather than those masterwork iron spears and steel swords you had made for the militia to replace those junky copper ones.
Elves likewise simply apply social pressure to keep dissent in check (and kill and eat those who pose an external threat to the community as legends shows us when they eat enemy soldiers - threats to the community - after killing them.) This includes exiling internal threats altogether, forcibly removing them from the community and making this a non-issue. They are also not very likely to come into conlfict with most things our civilian dwarves might have to fend off, being at peace with wildlife.
Humans could have a serious issue with this, due to their wildly varying values, and goblins are virtually guaranteed to have regular infighting between two armed mobs squabbling for authority. It could be the norm on some worlds for humans to be comprised of many city states that all broke apart from an original central government while many goblin sites simply can't wage external wars very often because they're too focused on suppressing internal threats.
Plus, now if needed we can potentially supplement the militia via mercenaries, who typically bring their own weapons.
Also, it's kinda fun to imagine how having this could affect gameplay - a band of unruly outcasts or armed refugees show up, and your piddling militia gets backed up by the miners and woodcutters of their own accord instead of having to draft them (and bypassing the issue with conflicting uniforms,) turning the tide their your side's favor.
Maybe one dwarf who was already on edge assumes a dude who bought an old sword recently is there to kill him and attacks him with a kitchen knife and it turns into a riot as both sides' friends try to break up the fight before the fortress guard can respond? (
Urist McStressedTheFuckOut is violently lashing out at Urist McNewPurchase in fear!)
Two drunken idiots in the tavern get into an argument and the chisel and hatchet come out and the two come to blows - and one goes to the hammering block because he slammed his chisel in the other dwarf's skull. (Urist McMurderer has felt
absolutely depressed due to murdering someone in a rage. Urist McMurderer is
is experiencing mortal fear due to his sentence.)
Of course, the way to appease both camps is via decrees from a noble (mayor or baron+) banning dwarves from owning personal weapons (resulting in confiscation and return of the weapons to the militia/Fortress's stocks,) or from forming unsanctioned militias (with offenders being jailed for a time afterwards,) or via a setting we can turn on or off at will in the int settings.
For example, a decree screen with one decree mandating civilians arm themselves, a decree banning unsanctioned possession of personal arms and a choice of punishments (beating or jail time and duration of the latter,) or simply lifting the decree, allowing dwarves to chose if they arm themselves or not.
Iunno, food for thought
Other 'self-defense' weapons & work tools that could be used as such could be mallets for masons and carpenters, hammers for carpenters/masons & smith, sickles for herbalists and farmers, and perhaps whips for animal trainers. Sickles and hammers of course would have to be fashioned from metal, but could use the 'two items from one bar' idea that I floated earlier, and mallets could be made out of wood as well as metal, while whips would be made from leather (really, they should be made out of leather already) Daggers and cudgels as a sort 'general purpose' self defense item.
Staves too, particularly for humans and elves.