I've done some thinking on the subject of what traits in music I enjoy. If you're as bold as to separate musical elements into two major categories, one being rythm and one being melody, death metal as a musical style focuses almost exclusively on rythm. Doing so you open up for a lot more focus and creativity on the rythm aspect of music which makes for some innovative stuff. Growl vocals only takes this further so not to revert focus.
I'm not the most avid listener to death metal, though, I listen to a lot more than the average guy and most likely more than the average metal fan too. I don't dress according to the music I listen to, don't choose friends according to it (though I have people I associate with, probably just cause we share musical preferances) and don't act according to it. This probably isn't what you're after, but I'm betting it stands true for a lot of people. As far as attitude goes, I don't know if you're hypothesis is that aggressive music fosters aggressive behaviour or not, but similar psychological studies, without being able to say anything conclusive, show a trend towards the opposite, if anything.
And if your thoughts go towards the Norwegian black metal scene in relation to my last point, remember that those were only a few individuals in an otherwise relatively large scene.
Yeah I dress like a prep, and most of my friends in high school didn't know I listened to any form of metal. I'm also an incredibly passive person for the most part. My personality traits reflect pretty much the exact opposite of what most people would expect the stereotypical Death Metal or Black Metal fan to portray.