Pretty much the same thing with metal.
Person: "It's all about blood and guts and Satan and being a racist asshole."
Me: *shows lyrics to a few songs off Death's Human, Cephalic Carnage's Xenosapien, Bathory's Hammerheart and Burzum's Filosofem*
Person: "Nobody even talks about vikings, society, aliens or alcoholics anyway so that's pointless."
So now whenever I'm wearing a shirt and they can read the logo and ask if it's a band about Satanism and gory misogyny, I just say yes. It's useless to try to convince them otherwise if they're too arrogant to give anything a chance, so just let them miss out on a lot of good shit. That's their fuck-up.