Good question, though I understand with respect to FGM there is dissent even within the culture about the practice. Amnesty's page on FGM might make a helpful overview for those not familiar with the practice:
www.amnestyusa.org/Stop_Violence_Against...2=39&n3=1101
For my part, I think normative readings of cultural relativism are false, and that respect for cultures, ethnicities, nationalities, whatever, does not extend to turning a blind eye to everything they do.
Hence I'd argue that you're not wrong at all to say that something like FGM is a violation of human rights, and ought to be approached as such by the rest of the world.
td