One more point has just occurred to me.

Even cultural engineers who are well aware of the risks and difficulties of modifying and building cultures from scratch may be forced to do so for other reasons. Natural selection creates marvelously adapted creatures (and cultures), but the casualty rate is pretty high, most of the competition dies trying, even most of the "good" ones. The space colony example I brought up may be a very expensive one-shot deal. At best, we may not be able to mount more than a handful of these expeditions. We may not be willing to chance them falling apart in disorder or violence or stagnation.