I dont. (well actually I do but that seemed like a fun way to start the post :P)
Yes, its true that to an extent you *can* choose what you're like, but there are influences to your personality outside of yourself, and that has to be accepted as well.
For instance, have you noticed that most child abuse cases find somewhere along the line that the abuser was once on the recieving end?
And why else do prim and propper families churn out prim and propper kiddies that say "oh that's ok" rather than "yeah you better be" (re someoone sez "sorry").
I'm not saying that somone is entirely moddeled by the stuff around them, but it can have an effect.
So you cant just shut GoldenBunnie down for voicing his opinion (although I must admit I didn't see the point in his post... :P)