The moral issue here is in regard to the knowledge of outcome of the trip. Generations will be sent into space with inevitable death and no ability to avoid that fact. Somehow the advancement of the human race, an idea that they have never experienced or have any reason to wholly pursue, will fuel their lifelong hard work in order to see that the mission is complete? Why would a ship of already dead people want to contribute to the success of the trip if they could never see any positive outcome. Maybe a computer could control the ship and only give food when work is completed?

The feasibility of the mission is not the question, only the ethicality, although the method the mission is carried out raises many ethical issues.

A common idea in this thread is that there have always been people who make personal sacrifices to advance humankind. Though, this is for the possibility of individual gain. Would the New World have been colonized and humankind "advanced" if there weren't tremendous benefits to be had? I can't imagine a scenario where there isn't some positive to willfully giving up their life; weather it be for their families, money, nations, or stakes for a greater reward.

Sending people to their unavoidable deaths is unethical because it robs people of the choice to risk their lives for any benefit, not to mention the pain of having children knowing they will die with the same lack of freedom.