Child, I'm sorry to tell you that the world is about to end. Most likely. You see, this madwoman has designed a doomsday machine that will end all life as we know it - painlessly and immediately. It is attached to a supercomputer that will calculate the 10100th digit of pi - if that digit is zero, we're safe. If not, we're doomed and dead.
However, there is one thing you are allowed to do - switchout the logical trigger and replaced it by a quantum trigger, that instead generates a quantum event that will prevent the bomb from triggering with 1/10th measure squared (in the other cases, the bomb goes off). You ok paying €5 to replace the triggers like this?
If you treat quantum measure squared exactly as probability, then you shouldn't see any reason to replace the trigger. But if you believed in many worlds quantum mechanics (or think that MWI is possibly correct with non-zero probability), you might be tempted to accept the deal - after all, everyone will survive in one branch. But strict total utilitarians may still reject the deal. Unless they refuse to treat quantum measure as akin to probability in the first place (meaning they would accept all quantum suicide arguments), they tend to see a universe with a tenth of measure-squared as exactly equally valued to a 10% chance of a universe with full measure. And they'd even do the reverse, replace a quantum trigger with a logical one, if you paid them €5 to do so.
Still, most people, in practice, would choose to change the logical bomb for a quantum bomb, if only because they were slightly uncertain about their total utilitarian values. It would seem self evident that risking the total destruction of humanity is much worse than reducing its measure by a factor of 10 - a process that would be undetectable to everyone.
Of course, once you agree with that, we can start squeezing. What if the quantum trigger only has 1/20 measured-squared "chance" of saving us? 1/000? 1/10000? If you don't want to fully accept the quantum immortality arguments, you need to stop - but at what point?
No, not really. I mean, it's not that far from something I said, but it's departing from what I meant and it's not in any case the point of my reply. The mistake I'm making is persisting in trying to clarify a particular way of viewing the problem which is not the best way and which is leading us both down the garden path. Instead, please forget everything else I said and consider the following argument.
Theories have two aspects. Testable predictions, and descriptive elements. I would (and I think the sequences support me) argue that two theories which make the same predictions are not different theories, they are the same theory with different flavour. In particular, you should never make a different decision under one theory than under the other. Many Worlds is a flavour of quantum mechanics, and if that choice of flavour effects ethical decisions then you are making different decisions according to the flavour rather than content of the theory, and something has gone wrong.
Everything else I said was intended solely to support that point, but somewhere along the way we got lost arguing about what's observable, what consitutes evidence and meta-ethics. If you accept that argument then I have no further point to make. If you do not accept it, then please direct comments at that argument directly rather than anything else I've said.
I'll try to address the rest of your reply with this in mind in the hopes that it's helpful.
You could equally have said "If your interpretation of the physics of raindrops involves fairies". My point is that no-one has any justification for making that assumption. Quantum physics is a whole bunch of maths that models the behaviour of particles on a small scale. Many Worlds is one of many possible descriptions of that maths that help us understand it. If you arbitrarily assume your description is a meaningful property of reality then sure, everything else you say follows logically, but only because the mistake was made already.
You compare Many Worlds to fairies in the wrong place, in particular post-arbitrary-assumption for Many Worlds and pre-arbitrary-assumption for fairies. I'll give you the analogous statements for a correct comparison:
The people of other worlds do not merit consideration because it is impossible to get evidence of their existance.
If we accept fairies...
... the sight of a raindrop falling is evidence that there exists a fairy a short distance away.
Taboo "justification". Justification is essentially a pointer to evidence or inference. After all the inference is said and done, the person who needs to provide more evidence is the person who has the more un-parsimonious hypothesis. You reject fairies based on a lack of justification because it's not parsimonious. You can't reject Many-Worlds on those same grounds, at least not without explaining more.
The difference is that the fairies interpretation of raindrops has different maths than the non-fairy interpretation of raindrops. When the math... (read more)