Calling extreme metal screamo is like calling anyone from Europe an Andorran
^screamo/death/deathcore/djent=/=heavy metal
Until people have listened to Iron Maiden and Judas Priests, then they do not know what true heavy metal is.
Also from what it looks like, people are generalizing music they don't really listen too. I don't listen to all genres of music, but I'm not going to hate something by generalizing. I will refuse to listen to certain genre by choice, but I' m not going to be all like "it sucks". Granted there are bad songs and genres that I don't like, but someone down the road likes it.
I could say all electronic music was beep boop beep boop wub wub dub dub wub
and all rap was "Drive by and gun dem bitches, smoke them like bitches, life in the hood!"