Let's say that across the multiverse all versions of you are going to collectively live for 1 billion years. Unfortunately, some versions of you will be tortured and let's assume that collectively you will be tortured for 10,000 years meaning that the measure your torture is 10,000 / 1 billion. But if you sign up for cryonics you most likely only get brought back in a world that has cured death and isn't evil. If many versions of you do sign up for cryonics say you live collectively for 2 billion years and are only tortured for 11,000 of these years so the measure of you being tortured is 11,000/ 2 billion.

Ah, it was the “probably a non-torturous society will bring you back, since they are more likely to be altruistic” assumption that I was missing. Of course, it only takes one entity to bring you back for an eternity of torture to ruin this logic, as is the case in IHNMAIMS.

Infinity makes decision making really weird since infinity + 1 is the same as infinity so if you are going to be tortured for infinity years it wouldn't be irrational to volunteer to be tortured for an extra year.