I mean undesirable and unethical are not the same thing. I wouldn't really even place an ethical question on a fish, unless maybe they live in an aquarium and know better or something (like eating their handler, assuming living conditions are good). Not even moral questions really, though a hungry fish is probably acting pretty morally to meet its base needs TBH.
That said, if there was a neck-snapper-fish I'm pretty sure people would seek it out. And they'd say stuff like live by the fish, die by the fish.
I mean if I was in the ocean and a shark just wanted to grab a bite to eat that's just fine. I can't really swim anyways so I guess that'd be preferable. Just as long as they're quick about it.
Also I hear sharks are really smooth, so that's nice.