Maybe the issue is that people assume that a randomly selected population would consist of US citizens. What if you picked Japanese? They did well during covid. An they are know for having a strong communal responsibility. Maybe the average US citizen is just a bad choice for a generation ship? Then again given the choice between sending foreign citizen's or sending no generation ship would probably result in no generation ship bring launched.

People from latin america might be a good match - last time the fleet of generation ships not only reached the destination in sufficient number, but one of them even ahead of schedule[0]!

[0] https://revelationspace.fandom.com/wiki/Sky_Haussmann

> The question is "Could we create a cadre of 400 highly effective people that could sustain a colony on a spaceship?"

For a generational ship, the question becomes even more complex because you would have to build a culture of expertise that can sustain itself over multiple generations.