That murderous example is an example of cultural appropriation but trading food and ingredients and whatnot did happen between places as well.
I explained why it's harmful in my previous post. You aren't respecting the *thing* if you're just wearing it for fashion. Wearing a band shirt isn't in the same vicinity as this because Metallica isn't a culture or religion and metalheads sure as hell aren't an oppressed group that are being killed for liking a certain genre of music.
I'm not going to say it's anywhere near the same thing, but there's a significant enough number of 'metalheads' that have been beaten/killed/etc just for being a metalhead.
As a personal example, my friend got straight up beaten in the streets for it. He now has false teeth at the age of 26.
A few weeks ago a group of arseholes went into a bar I go to
(a metal bar) just to cause hassle. Some guy left in an ambulance because he got massacred with a bottle, apparently just because he likes metal
(I wasn't there at the time, though I was around to see the aftermath).
Last year some guy got beat in the streets. Aside from the beating, they broke his legs and dragged him into the middle of the road before leaving him to die
(though a car saw him laying there and phoned an ambulance). I think it's obvious what sub culture he belonged to...
Those are just three examples local to me
(and I only included 'serious' cases. There's way more 'less severe' ones), but the most famous one I know of is Sophie Lancaster who got beaten to death because she's was a goth
(which is relatively within the same 'group' as metalheads) as well as her boyfriend
(I believe) suffering major injuries
because of what they wore/listen to.
Like I said, I'm not saying it's the same thing as it happening based on race/sexuality/etc, but it sure as hell does happen. It's not like you're getting people going to clubs with machine guns and mowing them down, but they're still targeted more often and usually more violently than most other 'groups' based simply on what form of entertainment they enjoy
(OBVIOUSLY I'm not saying they're targeted more than gay people).