that's because they're a form of technology, and mechanically, pretty cool
but "defiling" them is not an issue, any more than it would be to put an MLP case on a phone or an MLP sticker on a laptop
how?
the rifle is a relic from /world war one/. it is not the same as a cheap laptop you can buy at nearly any hardware store, it is a very uncommon and, should it actually work, very expensive weapon, and likely would have some huge sentimental value for the anon's family, if not the family of the john doe who originally used it.
what this moron did was take a perfectly good, expensive, and rare relic, and then painted the damn thing blue and slapped a rainbow dash sticker on it. that p much wiped its value clean.