imo you guys are making it a bigger deal than it really is
guns are not like, important artifacts or anything. they aren't a real part of history. they're just mass-produced weapons
Depends on the period of history they're from.
Last 50 years, perhaps you're right.
But then you get WW2/WW1 weapons, and there aren't billions of the things left in decent conditions. And they're a connection/record of a violent period in history where lots of people lost their lives.
Defacing something like that is still a pretty stupid and tacky thing to do. Sure, there are plenty of worse things you could do to an old gun, but it doesn't make this any less cringey. It would be equally as bad if someone painted them with Pokemon, or Spongebob Squarepants, or Call of Duty logos.
The pistols and shotguns above are just generic things though. You get plenty of guns that are produced with stocks and other parts decorated in colours and pictures for children.