Not everything. I mean the entire Tysha incident, what did that gain him? What war did that win him? That seemed to be pretty evil just for the sake of being a bastard to his son whose only sin was being born.
Like most in this series he is after power and he is also driven by his legacy, he claims it is about his family name, but lets face it all he really cares about is what people will think about him personally. That is why he hates Tyrion so much, yes his wife died as a result of childbirth, but in the end Tyrion's physical appearance is an embarrassment not just becuase others have and do make fun of him, but because Tywin is embarrassed that something "like that" could be produced by his loins. He believes his enemies will see it as a weakness, Tywin sees it as some sort of stain on the Lannister legacy.
He wouldn't let his son (regardless how much he hated him) to marry a lowborn girl. It also served a lesson to Tyrion to not do things on his own.