Why is murder wrong if Many Worlds Interpretation of Quantum Mechanics is true?

[FlatAssembler]

Fish do feel pain, which is why they're anesthetized and/or stunned (among other things) before the kill in operations with an ethical focus.

I think the scientific consensus is that they don't. And the arguments for that are fairly easy to understand:

They do not behave as if they felt pain: a fish with a hole in its fin continues swimming normally, rather than trying not to use that fin. Also, fish do not have the neuroanatomy necessary to feel pain: they have little or no type-C neurofibres, which are necessary to feel pain (we know that because people with congenital insensitivity to pain have fewer type-C neurofibres), not to mention the brain structures.

If fish can suffer (be it only physical pain), then the right thing to do would be to stop eating them.

[Foxaèr]

If a world exists where murder isn't wrong, then it's not wrong on that world. It's only wrong to the outsider looking in and visiting that world.

[The Grand Nudger]

Yeah, sure. The most ethical decision might be to source our food pain free, cruelty free. The practical realities of our situation may not allow us the most ethical or even any ethical resolution on that count, though.

So we negotiate. Try to do some less shitty thing. We may, for example, have to do something that can cause pain. So, if we’re going to do that- we can at least do it with that pain in mind. Hence the niche, which may in fact err on the side of caution where no pain exists.

I could point out to a customer that the usual killing method is no more or less likely to cause more or less pain than these other processes- but I wouldn’t- because Id never see them again.