i'm hesitant to wade into this debate, but i really don't think cultures and value systems are relative at all. i used to, and certain elements are relative, but there are fundamental values that are worth fighting for and others that are generally abhored by most people. cannibalism, incest, rape, torture - these are particularly nasty ones that you would have a tough time convincing me are relative.
on a less offensive tier, the subjugation of a gender, the exclusion of minority voices, the repression on the popular will - these are also values i think are terrible and i think we should be working to rid the world of. sure, some degree of cultural understanding and relativism is necessary, but we can't just ok everything because some people are different. we have the right to judge - in fact, i actually think we have the moral duty to do so. not necessarily to enforce, but certainly to object and to give people the possibility of other realities, expecially in situations they cannot escape.