Hussar
Legend
If it is slavery then who owns who?
Hrm, you are forced into servitude for life from birth, have zero choice, cannot resign and cannot leave. In what way is this not slavery? Not only that, but your children, your children's children and their children as well are also forced into servitude with no recourse. Oh, you don't want to have a baby with that person? Sorry, too bad, we need your DNA. Oh, you're gay? Again, too bad, we need your DNA. You don't want to be an engineer? You want to be an artist? Too bad, you have no choice since the last person who died so that you could be born was an engineer. That's what we need.
Oh, you want to have more children? Nope, sorry you have no reproductive rights. No rights to personal freedom. No rights to religion. No rights to free speech. It's unlikely you'd have any rights to self determination.
How is this not slavery? It's even more insidious than the usual sort of slavery since slaves on Earth can revolt and be freed. You will never, ever be free, nor will your children or their children, until, dozens of generations down the line, your decedents manage to reach the destination. And, even then, they still likely won't be free because they'll be forced to create a new colony, whether they want to or not.