Nah, it has nothing to do with aggression, violence or crime. That's a misconception of outsiders who hear the loud music and growled vocals and assume they are an attempt at intimidation. In truth it's just a very strict art form, and I know it's hard to see it as an
art form but that's what it is. It has a certain range of emotions that it chooses to express but it doesn't really have a message, like, go out and eat some babies alive.
There's going to be exceptions to the rule of course, but the majority of kids who dig this stuff are nerds. They finish school and go into a STEM field in science or work in the industry as coders. Like, my best friend in high school was into Cannibal Corpse and splatter gore bands like that, and now he's a doctor. And, hey, I was all into Black Metal and now I got a PhD in computer science. Yeah?
In fact, for me and my friends at least, being into this stuff was also a way to draw a clean line between us and the kids who wanted to grow up and be rich bimbos like their moms and dads, that sort of thing. Not that my friend who's a doctor is poor, but in my school at least we had lots of the kind of kid who comes in with expensive new clothes and brags about her dad's car or where the family is going skiing this Christmas, and it was fun to flip them the bird every day by coming into school with a Kreator t-shirt with a severed head sinking into blood (albeit very stylised; and Kreator aren't death metal). So for some kids at least there was a bit of that. Nerd solidarity, like.