Because being friends with you is like one minute being hugged, and then the next minute slammed against a wall.. it is not a very good feeling.
I fancy that feeling as much as I fancy a knife in my back.
I would rather be totally dispised by you then have to tread on eggshells constantly. Sure a true friend will have consideration for feelings, but I don't say anything offensive anyways.. unless it comes to sex where I joke. Quite honestly I would rather have someone that I can be myself around then someone who doesn't know me well enough that they know whether I am joking or not.
That is just me.