Don't get me wrong, if one person is secretly planning to stalk, abduct, kill, cook and eat people, then yes, I think that should be disclosed to the proper authorities and the partner.
However, if someone is just fantasizing by themselves about killing and eating someone and genuinely has no intent or even interest in actually carrying out any such thing why would that come up? If someone fantasized about, I dunno, being smacked around by Sophia Vegara (one of her Pepsi ads was just on; I have no fantasies regarding Sophia Vegara), should they be required to disclose that?
I basically agree with this about most sexual fantasies. Who among us shares every single fantasy we have with our partner, even ones that involve them? Say a woman fantasizes about her husband getting it on with another man while she watches or participates, and she knows darned well he's not bisexual
or polyamorous, so it's never going to happen? She's really fine with this, and has no intent of ever asking him to do this and confines her fantasy to reading a little erotica or watching a little pornography that pushes those buttons for her.
But what if he finds out she's sharing these fantasies with a community of people who are into polyamory and bisexuality, and she's spending an inordinate amount of time indulging in these fantasies and hanging out with this community, maybe even to the point where it's impacting their real sex life and relationship?
That's where it might start to feel a little strange. Not because these fantasies or the lifestyle is wrong, but because it's gotten to the point where it's taking over her life. And this would be even more so with fantasies that entail actually harming or killing someone.
What I'm saying is it's one thing to discover that my husband has a thing for blondes with big breasts and he's been doing some creative photoshopping with pictures of me to make me look like a large-breasted blonde. If he swears he'd never cheat on me and has no desire for me to have a boob job or dye my hair, believing him (if he's lying) could end in heartache, but not in my death. But if I find pictures of him cooking and eating me, and I discover he's involved with a cannibal fantasy sex group, even though he swears he'd never really do this, the price of this being a lie is much higher.
Or to consider another issue. Think about how most people would react if they found a stash of animated child porn on their partner's computer. Even if the partner swore they'd never really do that to a kid (and since it's animated, no actual children were harmed in the creation of this porn).
I don't think I could continue the relationship, and I might be really worried. The issue is, of course, is how can law enforcement differentiate between something that's really just fantasy, even if it's an obsessive one, and something that's morphed (or is in the process of morphing) into an actual plan? I'd guess expert witnesses would be involved here.