Well obviously in western society in three major religions its taught to us from childhood that its a dirty sinful thing... The bible, Koran. and Torah are replete with stories of its sinful nature and orders to kill anyone we catch indulging in it... I mean there is a big reason right there...

However in the more modern era there is the fact that we are taught by medical doctors that its an unhealthy place/spot on the body. When I was in school I seriously freaked my health teacher out with to many questions about the anus and anal penetration Later as any adult who suffer anal injuries I found most doctors (non proctologists) where very uncomfortable and sarcastic about anal examinations...

Poopy smells bad... as Dr Kellogg said in Wellville... "Your stool is runny and foul smelling..." Not mine of course mine is as big and firm as a brick with no more smell than bread fresh from the oven... Hahah

shit is shit its bad..biological waste that carry harmful micro-organisms.

Dirty things are cleanable. We do that all the time with other things. When it gets dirty again, clean it again. This is not a strange concept.

I'll just leave this here lol
http://www.youtube.com/watch?v=q1wwe9-be2Y

That is... hilariously depressing.

seems obsolete since shit seems to be coming out of peoples mouth these days.