Yeah, we should colonize other planets.
1- To prevent a comet or asteroid from killing all of us off.
2- To get the resources from the other planets. (What is it? Earth first, we'll mine, log, and farm all the other planets later?)
3- We will eventually run out of room here for everybody. And unlike some people, I'd rather use that population to colonize other planets than kill them off like China is currently doing and others want to do.
4- Since we apparently can't all get along here on Earth, maybe separation of a few AUs would help matters. It gives those of us who don't like things the way they are a chance to make things the way we want them. Sorta like how the US came about, just on another planet. You can have one planet that subscribes to one thing, and another that subscribes to something completely different, and living there (sorta like now) is completely voluntary, and if you don't like one place's ways, go somewhere else. Gives us all options.
5- Exploration and colonization is kinda in our blood. It's what we do.