As an enthusiast of such things I can say that it's a nice thing for North Carolina to do and doesn't hurt anyone. It's not necessarily about it being an extension of our genitals, it's more that literally hundreds of historical weapons have been destroyed when they were confiscated in the UK as laws were tightened, including very rare pistols or rifles that should have been in museums. That law doesn't really have glocks or something in mind as much as it does, for instance, a Luger your grandfather brought back from the war or something that would be confiscated and destroyed in the event that gun control tightens up, as it probably will one day. We are talking antiques here, after all. Some of them extremely valuable.
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.
You may suggest that guns that are only 10 years old are not antiques or historical and are not worth keeping. Indeed, some gun laws are built around clauses like that. Some of these guns though can be limited editions that are worth keeping for collection elsewhere, or even guns that have emotional significance for the shooter (such as their "first gun", or a gun that belonged to someone) and they would be quite upset to see them destroyed.
And quite a few guns might have emotional significance to the
victims, who would be upset to see them resold to the public.
That said, I think stuff like illegally modified TEC-9s are historical pieces that are worth keeping examples of and should not be destroyed. Like the Apache pistols carried by French gangsters in the 19th century, they're significant in that they were the weapons of choice for so many criminals throughout the late 80s and early 90s. After all, what's the problem with keeping them if they're safely in the hands of the authorities? If there's too many of them, decommission them and sell them, or send them somewhere where it's legal to own them live. If there's still too many after you've done that, recycle them.
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.
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.