Following on from the 2005 objections debate here about multi-generational interstellar travel I want to put the ethical issue of ‘condemning’ future generations to a limited life on board the ship.
Basically the arguments against focus on the future generations not wanting to pursue their forefathers ambitions and having a limited life (not being able to have a wide selection of human social relations, being cut-off from Earth society (at least in a physical way)).
According to British anthropologist Robin Dunbar the amount of people we know and keep in contact with lies between 100 and 250, meaning there is a good chance on a ship with a starting crew of say 2000 people which of course will expand through the generations it is unlikely that a situation will arise where everyone knows everyone.
As for the idea that these future generations will be cut-off from the developments back on Earth this is potentially true should there be a communications malfunction otherwise audio and visual communication and learning will continue to be possible as well as uploads and downloads.
Comparisons have been made to past explorers setting out to find new land on Earth and colonising islands, effectively stranding their future generations to the island till the time came about that allowed travel much easier and faster.
In short I see absolutely no issue with setting out on a multi-generational adventure providing that the crew consisted of at least 2000 people.