I'm also convinced the reason this genre (Deathcore included) gets so much flak, is because it's brought back something we thought we'd gotten blissfully rid of when Glam Metal died:
Teenage Girls.
Let's face it, a lot of bands then, and now earn extra publicity points for having an attractive frontman. Would Bring Me The Horizon have gotten anywhere if they didn't have Oli "Fething teen Heartthrob" Sykes on vocals? Would Poison ever have hit it big if they didn't tart themselves up to make mid-80s High School girls all hot'n'bothered?
Not bloody likely, I say...
Of course, that makes all us basement-dwelling, beta-male troglodytes who couldn't even get laid in a "Omega Man"-type scenario very jealous. Hence the hate.