Necromancy is legal, Giok. I think you are thinking of necrophilia (not implying "thinking of" as meaning "considering indulging in"). Apart from finding it distasteful, I can't see who is being harmed anyway.

Incest? As long as (1) no child is involved, either as one of the parties or conceived as a result, and (2) full consent is involved, which is difficult to demonstrate when power relationships come in, I can't see the harm done. Perfectly normal in some societies, see ancient Egypt, also see Eric Gill. Not for me.

Bestiality? Can't see how a non- human can give meaningful consent, and I don't fancy the sheep round here, many of thm are Jacob's anyway. On the other hand, if we abuse animals so far as to kill them and eat them, why the hangup about sex?

I think informed consent is the key phrase.