Okay, I see what the issue is here.
Our political beliefs aside, one side is (using Wikipedia's definition) essentially stating what is needed is a Civil Protection/Defense program, which "is an effort to protect the citizens of a state (generally non-combatants) from military attacks and natural disasters." The other is functionally arguing against that.
This is different from putting everyone in the militia, which is functionally a dwarf site's standing army, being used for
both offensive and defensive operations. It might not be that in practice, depending on the player, but that's the function it fulfills.
Arguments regarding safety during interpersonal conflicts and Law Enforcement are valid criticisms, but they are also more pluses than minuses, addressed further below.
One argument is to throw everyone into the fortress's de facto standing army, which isn't really ideal, and does not take dwarves' preferences and personalities into account. This is in fact, one of the arguments
for allowing access to private arms irrespective of the militia, as it allows those dwarves foolhardy and whatnot enough to keep a weapon and fight regardless of what the player wants, to do so.
This seems to be irreconcilable.
Okay, well. How about a middle ground? Civil Militia - An unorganized military force comprised of explicit volunteers. You have no control of who is in it apart from taking those volunteers out and putting them into the proper fortress militia. Their "squad" is shown on the squad screen not with names, but just as a number of however many dwarves are in it, and the leader is the highest ranking militia officer who is on map and not incapacitated, which will usually be the Militia Commander.
This force can be activated and will follow kill orders presumably given by the officer they're currently tailing, and follow move orders given to that squad. The squad they're following for the duration of the incident will be marked with "CM" next to them in the squad menu, and when inactive, these dwarves need to wait until the militia has armed itself (negating the resource allocation argument further) before they can take any weapons if taking them fromt he fortress stocks, or further down the road, they may use weapons they made or bought, taking pressure of the Militia's armory some. If a threat appears, they will fight the threat while the more timid elements flee from the danger.
This also meshes well with vigilantism (as those same dwarves in this unorganized force will be the ones likely to try and take vampires, thieves, and murderers on directly by feigning sleep to ambush them,) and takes the "armed mob" concept and makes it functionally a player-ordered event. Additionally, these dwarves will use any barracks with an assigned squad and watch thier sparring and training sessions, allowing them to train without us having to add another space specifically for them - they can learn directly from the actual military in thier own free time.
This force cannot be used in offensive actions off site, and is not armored or given food and ale provisions like the militia, but it does provide a body of armed and "conflict compatible" dwarves to fight in an emergency plus allows those dwarves who "enlist" in the Civil Militia to functionally be an informal escort force for the general population, and informal sentries to deal with snatchers and kobolds.
If a real threat comes, they'll have a weapon and possibly some training to commit suicide with, since these dwarves would be liable to attack ambushers, zombies, and animals anyway, and might slow down the threat or even kill one or two attackers, in the case of invaders while the Militia is in transit to the problem spot.
While they might use these weapons on eachother in arguments and tavern brawls (or if they flip shit due to stress) this still gives a greater need to even having law enforcement in the fortress besides the one guy who failed a production mandate or accidentally violated an export ban, as well as potentially have a reason beyond "fortress is already collapsing" to have a Hammerer, as well as give the medical staff needed experience.
And to top it off, we can round this out with a configurable option to enable or disable this like temperature, weather, and invasions in general, giving everyone access tot his if they want it, and not having to put up with it if they don't.
Note, the above was put together with an outside observer's input, and so is largely clear of any biases on my end apart from the "rah rah, more violence, more chaos!" part of me that most of us have on some level with this game