I think the distinguishing factor is that it is (or could be considered) a victimless crime. If we're going to judge other cultures (and I think we should try, to be sure of our own convictions), then I figure we should make a distinction between crimes with and without direct or known victims.

For example, a country where gay people are thrown from rooftops and mountains, is easy to judge. The people performing the practice are aware that they're doing something cruel to a specific person, and the supposed crime they are punishing has two or more beneficiaries, rather than victims.