et cetera, are not well-understood enough to make claims about whether or not you should even care about the number of 'yous' that are living or dying, whatever 'you' think you are.

This argument from confusion doesn't shift the decision either way, so it could as well be an argument for signing up, or against signing up; similarly for immediate suicide, or against that. On the net, this argument doesn't move, because there is no default to fall off to once you get more confused.