I don't think there's been a rash of overzealous cops destroying great-great-great-great-grandpappy's musket what he done used in the War. For one thing, the number of musket-related (or muzzle-loading rifle, or whatever else) crimes is not really a thing. I'd wager the majority are cheapass .357s (the infamous "Saturday Night Special") and 9mm like the TEC-9.
I wasn't talking about muskets at all, there's no question about them being safe. You'll notice I didn't mention muskets for that exact reason. There's guns that are just 10-20 years old however that are historical and do have great significance for collectors. I'm going to go into this again later on, but you have to remember that these laws do not discriminate well enough between what is a historical weapon and what is not.
Indeed, even then it can be ineffective because what is plentiful then can often be extremely rare and significant in the future - examples include all the WW2 bolt action rifles that were floating around in the UK prior to our laws being tightened. Nowadays they're rare and super expensive - take the K98. Since restrictions increased, shooters just stopped firing them in competitions because it was too difficult to jump through the hoops and handed them in for destruction or sent them away somewhere. Nowadays they cost up to 1000 pounds (1600 dollars). In the USA they cost 200 dollars, around 123 pounds. A good example of a Springfield 1903 rifle with a sniper scope would cost £10,000 in the UK, AKA $16,000. In the USA they cost around $2,000 dollars or $1237 pounds.
I know you laugh at it and can't believe it but that is a very possible future for American gun owners. I know your frustrations lie with the gun lobbies which are far, far too powerful in the USA, but we have our own gun lobbies in the UK. They just stopped caring as much about certain guns. We actually have our own NRA in the UK but as soon as they said "we don't need semi automatic rifles" all the SLRs, SKS's and Garands went out the window. Rather, our lobbies have got their little niche that they're comfortable with - shotguns, .22LR rifles, bolt action/straight pull rifles for hunting. The American gun lobbies are getting themselves comfortable around a different set, specifically one based around handguns and shotguns. The handgun lobby is the most powerful of course and the one that has the most to answer for, that's why they're distracting Americans by trying to focus their attention on scary-looking "black rifles" like AR-15s rather than the guns that are used in the most crimes.
The guns that are used in crime, including mass shootings, are primarily handguns like Hi Points, Saturday Night Specials or some kind of Glock if the person intends on "using" the gun a bit more than holding up a petrol station, as you say. They don't really need to be destroyed, but that's not such an issue for me. My concern is that the law that is going to be created in the place of the Protect the Guns law or whatever it's called will be too broad-sweeping and involve destruction of guns that other people could keep comfortably, or would be very valuable to collectors now or in the future.
And quite a few guns might have emotional significance to the victims, who would be upset to see them resold to the public.
I think they need to get their heads sorted if their beef with the tool rather than the perpetrator is so great to the point that they can't cope with them being resold to a collector elsewhere who, we can generally assume, won't use it in a similar crime. Tough I say, I'm sorry. I'd prefer to protect potential victims in the future by ensuring that background checks and other forms of gun control are more effective rather than bending over backwards to appease a distraught family. I always say that victims' families should be the last people to decide any kind of legislation because, frankly, if a member of my family was murdered I don't think I'd be in any frame of mind to be influencing legislation for 10 million people. That goes for any crime, and I've thought that way for a very long time for a number of reasons, well before I started looking into guns more before you accuse me of being an insensitive gun nut.
The thing is, you're looking at this from the standpoint of the UK, where guns and gun purchases are indeed rare and privately owned firearms thus have a much higher chance of being an heirloom weapon.
Actually I'm looking at this from the standpoint of a person who takes an interest in collecting firearms of any sort. There are people like me all over the world, the vast majority in the United States. Practically every single person who owns more than one gun will have one with emotional or historical significance to them - whether it's because it's the "first gun" they had, or because it's their favourite (don't underestimate that), or because it belonged to their friend/brother/sister/uncle/mother/father/grandfather, or finally because it has a particular history. As an example a friend of mine has a Swedish Mauser bought by the Finns who used it in the Winter War against the Soviets. It's been deactivated in the old specifications so that means it's as good as live, but there's a little bar in the barrel or something. That means it's been passed around, changed hands for a long time and accumulated history like any other antique, and it's also around 10 times more valuable than the price that he bought it for. That's the kind of thing that you might see in a crusher somewhere in 2070, if not a bolt action then a handgun or, most likely, a semi automatic equivalent.
This is America. Like most every other product we consume with gusto, our guns are mass-produced and nearly disposable. People buy a new shotgun like they'd buy a new tennis racket or bowling ball. For fuck's sake, they might be on the same aisle as the tennis rackets and bowling balls! They're considered a "sporting good" by most retailers.
As they are in the UK also, albeit a heavily regulated one. I'm afraid though you aren't as familiar with the US gun scene as you think -
some guns are disposable, mass produced tools for hitting targets, shooting deer or committing a robbery. The people though that like guns enough that they will own more than one however tend to look beyond the cheap, 100-dollar handguns and the like and tend to buy things that are a bit more expensive, put more thought into it and so on. It stops being like buying a tennis racket at that point and becomes more like buying a new car, games console, PC and so on.
Those are the guns that will get destroyed along with all those dollar-a-piece crime facilitators that you're concerned about as soon as gun restrictions tighten, just as they did in the UK. These laws don't tend to discriminate much because legislators often don't think them through, as you've just done by just concentrating on one particular characteristic of the US gun scene rather than taking in the wider picture.
Of course if this was actually a serious problem and there was an enormous surplus of Hi Point handguns that were accumulating in warehouses somewhere, rusting away because the state couldn't give them away or destroy them, then by all means recycle them. I believe that there should be a degree of protection however for these guns to ensure that the vast majority of those that people could put to good use won't get scrapped.