The interesting thing about both of your examples, is that they themselves are both examples of people "defining what should be meaningful for other people." Female circumcision is a statement by a culture that sex should not be desired by girls. The one-child rule is a statement by a culture that quality of life for its existing members is more important than quantity of life for its hypothetical ones. In either case, individual members of the culture may disagree, but then will be forced to conform to the culture's mores anyway—
that is what we find repulsive about those policies.
As long as, on an individual level, people are free to choose their own utility function (as long as that function doesn't stop other people from choosing and partaking in their utility functions), then nothing else really matters on a grand-er scale. To put it another way: "cultural relativism" is wrong, but only because there is theoretically a perfect culture that allows its individuals to have individual relativism of ethics with a minimum of friction between individuals. The best culture is the transparent one people don't define themselves in terms of.