Like I said, ultimately it comes down to a situational thing that revolves around circumstances.
You can consider it a battle of Wills, and if said wills are based in positive or negative things.
If a Fetishist wants to be eaten, this is fantasy that will be crushed once reality sets in. Avoid that, unless indulging as the opposite is your fantasy...however know that you are inheritingly the wrong party regardless of the consent given before the deed.
If it is an Instinctual thing, such as Beastars and real world scenarios go; then it depends on your ideals and whether or not you which to be a slave to your Nature, or the master of yourself by living to a higher ideal that ultimately rejects your preprogrammed self.
If its some who thinks they wish it, but does not understand the whole of it "Death in Despair" then you should prevent this, by showing them the Reality of Death, and also Life, you should give them something to live for, or at least give them another option that isn't suicide.
If its in the Ideal of someone who truly wants to die, and begs for it; then you should indulge them on that because that is something that they understand, and still willingly choose. If you show someone suicidal the weight of Death and Life, you show the Reality of both, and they still desire Death, then oblige them and help in that for that is what they have chosen. However; you must make a sincere attempt in showing them the weight, because if you do not, then you are simply abetting someone who needs help to tick your personal box of selfish joys.
This is strictly in regards to sentience by the by; and not everyone has that sadly. Most people live according to their Natures, and have limited Sentience. You shouldn't prey on those people, you should seek to either pat them on the head, or try to Enlighten them to full Sentience. Its stuff I think about in Philosophy, just in metaphoric senses and not literal.