Quantum immortality sounds exactly like the mythical hell
And is about as real.
The idea of quantum suicide is that we should act as if we won't die, because there will be some future "us"es who don't die. But this argument is wrong because the person who makes the decisions isn't one of those future people - it's the present person, who is completely entitled to not want to die.
We can demonstrate that this fails even classically. Imagine a pill that, when taken, causes the taker to believe that taking the pill is a good idea. A rationalization drug. And suppose that this pill also causes violent diarrhea. Is taking this pill a good idea? The person who takes the pill would certainly say so! If one is to avoid similar entirely-classical silliness, one has to invalidate appeals to what future people will think as a reasonable way of deciding, and instead just make decisions according to the present person's preferences.
One response I've seen to this was "dying is not like a pill that modifies your judgement" - the trouble with this is that as modifying the output of your brain goes, putting a big hole through it is a highly effective example. Another possible response is that the present person is not "rationally allowed" to not want to die, for some philosophical reason. But that position is inconsistent with all our shiny theoretical models of what "rational choice" means, not to mention human behavior.
Ultimately, understanding quantum suicide boils down to understanding the difference between future utility and expected utility.
Or you could simply consider all of those versions of you with holes in their brains sufficiently different from yourself as to be no longer considered "you", making it so that you only care about the "you" who lives.
The above seems to me like a fairly defensible position. After all, as modifying the output of your brain goes, putting a big hole through it is a highly effective example, as you yourself noted.
Quantum immortality sounds exactly like the mythical hell: living forever in perpetual agony, unable to die and in your own branch of existence separate from everyone else you ever knew.
What if we can hack quantum immortality to force continued good health, and the mutual survival of our loved ones in the same branch of the universe as us?
It seems like one would "simply" need a device which monitors your health with biosensors, and if anything goes out of range- it instantly kills you in a manner with extremely low probability of failure. All of your friends and family would wear a similar device, and they would be coupled such that if one person becomes "slightly unhealthy" you all die instantly, keeping you all alive and healthy together.
We nearly have the technology to build such a thing now. Would you install one in your own body? If not, why not?
Who wants to invest in my new biotech startup which promises to stop all disease and human suffering within the next decade? Just joking, there is a serious technical problem here that makes it considerably more difficult than it sounds: for such a device to work the probability of it's failure must be much much less than the probability of your continued healthy survival. You also never get to test the design before you use it.