Why are new heavy metal bands so harshly criticized?

Slipknot, Korn, Disturbed, Avenged Sevenfold, Bullet For My Valentine, Mudvayne, and others are so hated by many today, and everyone says they "aren't real metal". how is this so? they seem to have the characteristics of metal, just with new styles. So Avenged Sevenfold and Disturbed are melodic and not crazy heavy like a "real" metal band such as Cannibal Corpse. did Iron Maiden, Judas Priest, Motorhead, and Black Sabbath just scream about killing and play blast-beats with guitars tuned down to the point where it just sounds like noise? no. were they melodic? yes. were they metal? yes. Avenged Sevenfold especially gets alot of hate and i think they are one of the most traditional new metal bands, with their Maiden-esque style. it bothers me greatly that most kids today think that metal is all about being brutal and whoever can scream more and play harder and faster is more metal. "Oh that Avenged Sevenfold is a metal band that whines and isnt even heavy. Whitechapel and Suicide Silence are as METAL as you can go!" is basically what people think of metal today. i really like the big names in the New Wave of American Heavy Metal. they keep the sound of the clic founding fathers of metal yet take it in new directions as well. and they dont have to be br00tal to me metal.