What is sodomy? Why do sooo many people hate gay and people?

Does someone being gay REALLY hurt other people? I'm bi-ual, but at my age the preference may change. I just looked at a forum and some people said some really rude things just because of a person's orientation. I think its dumb and there maybe a higher chance of aids but thats one reason why there is condoms. I mean seriously explain this to me, please?