why does...

why does politics and religion seperate so many people?.why are they such divisive topics?.what has happened to true debates,and true social discourse.(did I use that word right,sounds right)anyway,so what happened.how is it that a person can hate another person.just because of their beliefs?.all of the blogs I follow do not believe what I believe.I do not hate them.I still follow them.I once had a myspace friend,whom I found through another friend of mine.she was totally liberal,hated bush,republicans,and conservatives.her page and comments were against them.I asked her to be my friend,she accepted.it was cool,no probs,that is,until we started chatting together.I still remember the last comment I made to her.I told her how great we were getting along together,like carville and matalin.the very next day,I kid you not.she deleted me as a friend,set her myspace to private,and I never heard from her again.I asked my friend what happened.but she never gave me an answer.why am I telling you this.because I lost my one and only follower because of politics.I'm not hurt because of this,I'm just trying to understand why.if everybody had to agree 100% with another,everybody would be single.when do liking someone,wanting to be friends become a zero sum game,all or nothing.