When it comes to human sexuality, it is very hard to pin down a why. There are so many possibilities, and it can be some of all of them or a lot of a few. Anal sex is considered by the vocal majority as taboo or illicit, though this is changing. This makes us feel naughty, like we are coloring outside the lines. Somewhere way back in time I imagine this is where all of the different positions came from. To make sex something different, instead of the same old thing. With the advent of the internet sex/porn is readily availible to view for free, and many people take advantage of this. So again "regular sex" becomes the norm, therefore boring, so we look for something different. This brings us to the little tight puckered hole that is so close to where we spend our time during normal sex. As it is so close we start to get ideas so as to make an experience different. We start by touching it and after a time we progress to a wide number of activities that include the asshole. Most people know that it feels good but not why. It is because the anus contains more nerve endings than a vagina. This is why it can feel incredibly good if done correctly, or incredibly painful if not. When it comes to pleasure there is a concrete connection between the physical pleasure and mental pleasure. We are told from the time we are born that we must be good, so when we start doing something, or wanting to do something taboo we get a thrill because we get tired of being good. I think that some of us want to be naughty but because of our upbringing we have trouble letting go of taboos. This is where the domination comes in, I believe. It is my experience that a lot of women will do things when being dominated that they would not readily ask for. I think it is because that when all is said and done and all the orgasms are finished, when they look back on it they can say "I am not a slut, he/she made me do it, so it is not my fault". The is silly of course but we has humans look for reasons to justify our behavior in many areas, not just sex. I know this is long and rambling but I just wanted to add my views. A womans ass is my fetish and I myself have wondered why. I myself recieve pleasure form having my asshole stimulated. I know this is because of all the nerves located there, but it still does not explain my focus on the area.