Just to drop the link (http://forums.civfanatics.com/showthread.php?goto=newpost&t=329193)

Well, the worst is not the diplo thing , but the simple fact that you can liberate cities to civs that you are warring with :crazyeye:

Yeah, liberating cities to civs you're at war with outside of peace negotiations is just asking for exploitation. There's no sensible reason to do it.