Well, if quantum immortality worked, so would quantum insomnia, or quantum sobriety, or the like. Being distracted in the middle of the thought - there's you that weren't distracted, why you're not always him? Or: there got to be a parallel you that via sheer chance effectively did not advance a timestep, and he's more similar to you now than the one that did.

More generally, don't take things too seriously for mere lack of a counter argument. Fringe ideas are mostly discussed by their promoters, while detractors have bigger fish to fry.