Why are so many people ignorant when it comes to metal?

Whenever I discuss my taste in music with people, the second I say I'm into metal, (And by metal I mean, Slayer, Lamb of God, MegaDeth, Tempest, Cannibal Corpse, not that BFMV and A7X ****), people write it off saying, "Oh it's just someone screaming into a microphone, it isn't real music anyone can do it. First off, not everyone can do it, try holding a bear growl for more than ten seconds. Second, people who listen to rap can't really say anything on the subject, as real rap isn't anything more than a consistent beat accompanied by somebody rhythmically speaking without changing their tone of voice. No inflections or anything of the sort. Seriously people are ignorant, if you took 20 seconds to listen to the lyrics of a metal song, you would realize that the lyrics, while granted they are not always easy to make out, do have alot of thought behind them.