Cannibalism is pretty natural. It happens in a myriad of species. Some mammals, insects and I'm pretty sure even some birds.
Human sacrifice is a cultural practice. It doesn't happen in EVERY culture or even in a majority. It doesn't even happen in nature.
Homosexuality happens in nature. Or at the very least same sex couplings can be found in the world of insects, mammals, birds etc.
Do you have any other flawed examples that are unable to distinguish between that which is 'natural' and that which isn't?