Sure, if your worry is elbow room. But when people say we don't want to "put all our eggs in one basket" they're typically including things like nuclear war, killer asteroids, and gamma ray bursts.
Yeah, I was referring more to the eggs/basket issue. Beyond that, though, I think there's a lot more to be gained from colonizing worlds than digging into the earth. One is pushing outward, the other is retreating inward, and is very much a dead end.
