Depends on if they know/respect their history, Black Sabbath are generally considered the first heavy metal band, even within the metal community. But I do understand where you're coming from, my partner grew up conservative Christian and rarely heard secular music until she moved out, and then gravitated towards pretty heavy stuff, Dimmu Borgir, In Flames, Cradle of Filth, etc, and I played some older metal band for her and she was like "this is metal?" so I filled her in a bit on the evolution of the genre. Like, if you've mostly listened to extreme metal and then someone plays Danzig's "Mother" for you, that's quite a jump, but there's no doubt that Danzig was considered metal.