A quick google search yields the information that screamo is not metal and is in no way affiliated with metal. I would go so far as to say subgenres using vocal techniques closely resembling those utilized in screamo, such as metalcore, are not in fact metal. Yes it has metal in it's name. That, surprisingly, does not make it so.
For people who are unable to tell subgeneres apart and have a genuine intrest in learning more about metal, I would direct you to Metal: A Headbangers Journy. Tackles many aspects of the culture and music.
OT: Lots of people don't know metal exists, so not many hate it. Many people hate both things they have not been exposed to before and things that are abrasive. For most people, metal is both of these.
Too lazy to scroll up to find a qoute but, mysterious person above, I too am perplexed about the volume of these hate threads. It's not a new, nor very confusing phenomenon that people seem to be jerks when you present yourself as different.
To people saying metal sucks or is the only good music: kindly broaden your horizons and stop validating your tastes on an internet forum. I did that for a while too, and please trust me when I say you'll regret being a ponce in front of countless strangers over something as silly as music preferences.
To those saying anything about metalheads as a group in general:..... really? You dislike a form of music because the fans you have been exposed to at this point have been dicks? You assume, because of this, that all are dicks? It's obviously your opinion (and as such I have no business trying to change it), but I wish you'd at least reconsider talking to the next group of casual metalheads you're exposed to. No, not the "AX7 is the best" group (or whatever entry level group is big wherever you are), but the person who happens to listen to. That guy who enjoys the music, but doesn't feel the need to yell it, or even talk about it that much. That guy is awesome. You should exchange bands with him and have a genuine conversation about things both of you are new to.