Don't get me wrong I do agree that for guaranteed future existence of the human race we will absolutely have to colonize other planets. Imagine how different life would be if we had all been born a thousand years later
If we colonize other planets, what happens when they rebel and fight against us? Inter-planetary warfare.
Space Invaders, but from the other side - you're trying to get rid of that damn pesky defender keeping you from your rightful place as ruler of the world!
