I think population in itself is neither "good" nor "bad."

What makes a big population "bad" is the lack of resources, wealth and opportunity to support everyone. China and India are good examples, where the majority of their citizens live below the poverty line.

China was trying to change that by imposing a limit on the number of children per household to one, but all it succeeded in doing is create an orphan population of girls. Chinese traditions value sons more than daughters, thus many Chinese couples try to sidestep the one-child law and continue to try for boys, giving up any girls they conceive to avoid the government's wrath through orphanages, foreign adoption or abortion.

In an ideal world, if everyone has the resources and opportunity to maximize each child's potential (guaranteed quality education, employment opportunity, basic needs such as food and shelter), then a big population would probably not be a bad thing. But alas, no such world will ever exist.

Would colonizing space solve this problem? Probably not. Given access and free reign to other worlds, we humans would probably eventually overcrowd them too. If we do escape our solar system, perhaps we are destined to becoming the ultimate galactic cockroach. :-P