Designing society for posterity

(Continuing from the comments/discussion following an earlier post ...)

Generation starships: they're not fast.

If you can crank yourself up to 1% of light-speed, alpha centauri is more than four and a half centuries away at cruising speed. To put it in perspective, that's the same span of time that separates us from the Conquistadores and the Reformation; it's twice the lifespan of the United States of America.

We humans are really bad at designing institutions that outlast the life...