Space travel won't do us any good if we can't solve our problems here on Earth. We'd just be bringing them with us wherever we go. We'd be delaying the inevitable, and maybe there's something to be said for that, but I think we ought to learn from our mistakes instead of just running away from them.
Having said that I think it is invaluable that we reach out to the stars and learn more about what's out there, go to other planets (aiming for Mars is great and all, but don't shy away from Venus just because it's an uncomfortable reminder of what the greenhouse effect can do), and generally improve on and create new technology that can help us do this.
As others have said, we need to fix our own problems here before we migrate somewhere else. It's not necessary for us space travel. We just want to do that. Humans rightful place is on earth and no where else. But, if we do happen to go to a different place, we'll just create a mess there like we did on earth. In my view we'd be sucking the life out of the planet as we're doing here, which would just make us similar to leeches. But yea, I'm betting on we wouldn't be able to migrate to another planet because there not another one similar to earth that has been found yet.
This is silly. There are six billion people on the planet, and the people who choose to research space travel wouldn't magically be reassigned to fixing the world's problems if we suddenly stopped funding the space program. Researching the world outside ours doesn't create some deficit in people working to make things better.
I hope I live to see the day we colonize Mars. I'd even volunteer to go up.