Medieval builders built Catherdrals that they knew wouldn't be finished in their lifetime.
Heading off on a multi-generation mission with no guarantee of success is not for most people. But there are billions of us. I'm sure they would easily find enough people to crew a mission.
Having said that I worry about the sustainability of these projects. If these are not indefinitely sustainable on arrival, then future generations are doomed to die out with no hope of survival. I’ve no problem with a carefully judged risk, there are no guarantees in life, but there has to at least be a reasonable chance.
The whole "cruel to children" aspect is flawed. It only self-identifies individuals with a world view that is very earth-centric. We need a societal system where such a position is seen as an honorable one. That's why I liked the Antarctica bit of the submission. We ALL need to learn and change.