Um, there is already a thread talking about this. Please don't make new threads about something already being discussed.
And no, the Arc canot last forever, but its the best bet for humanitys survival, would you rather go on land that is infertile, unable to produce food, having to start over, with savage humans all around? The Arc cannot last forever, yes, but it also has important things such as water treatment facilitys, power plants, housing, and all of the such. The only way i see things working out, if EVERYONE on the Arc unites together, takes up arms, moves the Arc to land, and take it over. They would have a very powerfull military force, and could use what is on the Arc to support a new nation on land.