Let's Colonize Titan
I think that, before colonizing other planets, we should start by realizing that Earth can easily sustain human kind for the foreseeable future, given some pretty modest tweaks to our way of life (compared to "going multi-planetary" that is). If we start valuing quality over novelty, stop eating animal-based foods and re-organize to live closer to where we work, we can stop the consumption and that is taxing our ecosystem and cut energy use to manageable levels. If we re-distribute our wealth, population growth will subside. If we put pressure on our rulers, they will work to eliminate the nuclear stockpiles. There are simple solutions to most of our issues. Once we have solved them, maybe we can start thinking about spreading our species to other places.