But we can't unbirth you, and clever tricks like pretending you already die and we have an opportunity to birth you again won't help.

I'm not so sure; "you've already died and we have an opportunity to birth you again" isn't very relevant to the question of whether one should commit suicide or not, but it does seem, to me, to be exactly what cryonics is offering.

It seems like most of the external effects of my death happen regardless of whether I'm revived from cryonic suspension or not. Suppose that a piano is about to fall on my head, but at the last minute, a wormhole opens up beneath me, and I end up in the middle of the Delta Quadrant surrounded by friendly, English-speaking aliens. ;) Now, in this (silly) scenario, I happen to be alive and well, but everyone else saw me get flattened by a falling piano and thinks I'm dead. As far as its effect on the rest of the Earth is concerned, this is basically just as bad as if the piano actually did hit me: my family and friends will still grieve, etc. And since all I get is confusion when I ask myself if it is better for me if I exist or not, I don't know if I have a reason to prefer "piano + wormhole" to "piano + splat". (Ignore the effect my presence will have on the aliens.)