It's very rational for you to avoid privileging any single one of my copies, but for me it's very rational to privilege my own instance. And likewise, I wouldn't care which one of your copies thrive, but I would expect that you would hope your instance is the one that survives.

And I don't see how linearity has to do with self-preservation instincts. Maybe you are arguing that once we have several diverging copies the self-preservation instinct will change and be content as long as one copy still survives? I just can't imagine it.