I'm not sure my feelings change much after I bang a girl. Then again I don't really "respect" women or people in general, so there's nothing to lose in the first place. However, I try to treat everyone with courtesy and respect no matter what I feel toward them, unless they royally piss me off.
Plus, I do feel it's important to treat women well after they bang me so they don't associate bad feelings with sex. That's one reason women have such anti-slut defense mechanisms -- they hear of guys treating their slutty friends badly and so they clamp their legs shut. If guys treated sluts well, there'd be a whole lot more of them and we'd all be getting laid a whole lot easier.
Also, there's a certain subset of men who, deep inside, loathe themselves. So when a woman accepts him and has sex with him, he transfers that self-loathing onto her. Basically he says, "I'm a piece of sh*t, and if you slept with me then you're a piece of sh*t too." Often a man's feelings toward a woman after sex say more about what he thinks of himself than what he thinks of her.