The Mote in God's Eye is a great book. You should read it. Not only that, but the plot illustrates something interesting that few people think about. To make a long story short, aliens send a spaceship to Earth. The science is legit. They use a laser and a giant solar sail to send a spaceship lightyears away from their own world. The journey takes hundreds of years. Generations live and die on this ship.
Generations live and die on this ship! Can you imagine such a thing? You learn to talk and finally ask mama, "So you had sex with dad, got pregnant, and gave birth to me? Knowing I'd live and finally die in this giant tin can. You decided before I was born that your child would exist only as a breeder for some future generation that might one day exist on another planet. I'm here to do some shitty job, impregnate some other selfish creature that exists only to stuff steadily declining resources into her greedy maw so that in her own time she can crap forth another hungry resource devourer? And all this on the faint hope that someday some distant progeny might colonize another shitty world? Did you ever stop and ask yourself whether you had that right?
The funny thing is this...you don't have to be on a spaceship going to another solar system to ask the same questions to your mother.