That one's not going to carry a death penalty. It is true and obvious that mates would generally still prefer to turn without permission than let their mates die. The rules accomplish two things:

a) strongly encourage at least a good-faith attempt at convincing the mate first;

b) serve signaling purposes to human societies they later reveal themselves to ("no, of course kidnapping humans to turn them is illegal; it carries an N year hiding sentence, and if we can humanely arrange for them to serve it without said mate, we do", as opposed to "yeah, if one of us wants to snag and vamp one of you badly enough it's gonna happen and we'll throw them an engagement party, sucks to be you").