Considering the winning bid got only $5,000, I don’t think this is a serious experiment.
With that in mind, the isolation makes a great deal of sense. The only world those children of those children of the original volunteers would be one similar to what they had on the ship. And the only world their future offspring would know would be the ship itself. It’s as much of a social experiment as it is space exploration.
Of, course, consent becomes problematic at that point.
Eventually, you would also have to limit just how many people know there is an entire world of people who aren’t on the ship, or at least how much they know about the earth. With 2,000+ people - Hierarchies would build. Factions would arise.
Never mind the ethical questions about birth and death rates. And, by the time it reached its destination, if it even did, and let’s be honest, the odds of that are less than zero, either technology on earth would have advanced far enough that someone else would likely have beaten them there, or most of humanity would have wiped itself off the map.
All this is to say - why the fuck not give it a try? At the very least, it would rewrite the book on ethics.