Every genre can be effective when done correctly. I only like a few deathcore bands but plenty of metalcore...for deathcore, the first All Shall Perish is good, Man Must Die is good, Despised Icon, The Plasmarifle, and the Beneath the Massacre EP...all good or great. For metalcore, I'm a big fan of The Sorrow, Raunchy, It Dies Today (though it sounds like their new album will suck), Bridge to Solace, Faust Again, Parkway Drive (Sirens > KWAS to me), War of Ages, etc.
I think that both of these styles being popular is very much a fad propagated by labels and promoters as well as the bands creating the music to some extent...it sells right now, and that's why people do it. Some bands are good at it, and they should be lauded for making good music. No entire genre sucks or is for faggots or whatever, and anyone who thinks this can get the fuck off this board.