Perhaps the problem is not enough people take the idea seriously, which seems strange to me because so many people take anthropics seriously and, from my perspective, they both work by the same mechanism.
I'll add that considerations here should probably focus on measure since given that we don't find ourselves in the a timeline where impossible things have happened we should expect that a thing's measure can and does go to zero so that "quantum death" can occur.
I also suspect that most people are not familiar enough with the physics to have much to say here since much of it depends on developing a metaphysical interpretation of evidence that is still being actively debated.
I'm weakly confident that EA thought leaders who would consider seriously the implication of ideas like quantum immortality generally take a less mystic, reductionist view of quantum mechanics, consciousness and personal identity, along the lines of the following:
It would seem to throw a wrench into the discussion around the Against Malaria Foundation and GiveWell's recs: http://effective-altruism.com/ea/xo/givewells_charity_recommendations_require_taking/
TL;DR: Don’t worry about any of this, just treat world-splitting the same way you treat classical randomness.
I don’t want to give a full explanation right now, but I don’t think you should be very worried about this.
I think the right way to take many-worlds into account as a utilitarian is to say that your utility over the universal wavefunction is just a weighted sum over Everett branches, with each branch having weight according to the Born rule. If you take this approach, then it adds up to normality and you don’t care about the difference between classical dice and quantum dice.
If you take this approach, then none of the issues you mention come up.
If you instead believe that every Everett branch matters equally regardless of its measure, which is basically what is required for the quantum suicide argument to go through, then your morality ends up being totally incoherent, because the universal wavefunction is nonzero everywhere that isn’t impossible for a geometric reason (eg fermionic exclusion—the wavefunction always has zero amplitude for any configuration with two electrons with the same spin in the same position).
Either way, I don't think there's any good argument that many-worlds implies any of the conclusions you mentioned.
I know a reasonable number of people who have a good understanding of anthropics and QM, and I think all of them agree with me that many-worlds adds up to normality in this way.
You might be interested in looking at theories of anthropics like UDASSA.