There's an interesting case that I'd read about a few years back, in which Armin Meiwes, a German computer technician, made a post on a cannibalism forum asking if there were any male volunteers within a certain age range who wanted to be killed and consumed by him. He had received a few replies from people who backed out at the last minute, and Meiwes did not attempt to pressure them or force them to do anything against their will. After a little while, he received a response from Bernd Brandes, a man who was willing to participate. The two men met up, and on camera, Meiwes cut up Brandes's -- I can't find a good euphemism here -- and the two attempted to consume it together, before Brandes began to lose consciousness and eventually was mercy-killed by Meiwes, who proceeded to cut him up, freeze his remains, and consume them for the next little while (until he was caught and sentenced to life imprisonment). 

This is such an interesting case to me from a legal and ethical standpoint. What makes Meiwes such an interesting case is that it's not obviously clear that he's dangerous or even a bad person.  Giving him a sentence equivalent to that of someone who kills an involuntary victim seems somewhat unfair. It's important to keep in mind that Meiwes only wanted to engage in this act with someone who wanted to be eaten by him. He was not a danger to anyone else and, as far as killers and cannibals go, I think one who respects consent should get some credit for it. 

Now, of course, the other side of the argument is this: Sure, Meiwes sought consent, but surely he had to have known that he was taking advantage of whoever was volunteering to be killed and eaten by him. Rather than seeking help for someone like Brandes, he decided to take advantage of him and that alone makes him deserving of lifetime imprisonment. 

But the problem with this argument is that with sexual preferences or kinks, it's difficult to draw a line between what's acceptable and what "requires seeking help". With the line of argument above, we would have to (to some extent) criminalize domination in BDSM, saying that the dominant partner in the relationship should've sought help for their partner, because surely anyone who gets aroused by being chained or slapped or mistreated should be "helped" and not taken advantage of. 

Now, of course, taking a healthy human life is a crime regardless of how we look at things (I will leave aside for the moment the question of MAiD for patients with chronic depression). I'm certainly not suggesting that Meiwes should've gotten off scot-free, but did this crime deserve life-imprisonment? Should it have been less? Should we distinguish between consensual and non-consensual killing, where the law is concerned? Should the fact that he knew what the law was, be enough to make life imprisonment justified for him? Is the fact that he's much less of a danger to society than other killers play a role here?

I'm undecided.