Thought: 1 (Bad language alert)

Have you ever noticed how many insults/exclamations are associated with poo and bottoms? There are quite a few: shit, shitty, bummer, crap, arse (ass), bugger, just for starters. I wonder what the obsession is with connecting basic bodily functions with bad things? Poo isn't pleasant, and as a human product it's never going to get the media's applause like, say, breast milk, but it's not a bad thing, surely.