To me, it only seems logical that we should move to other planets. Once we're capable, we need to get on it. There's no reason we should just stick to our one planet, that I can really think of. The benefits would be great if we were to go to other places.

I was talking with Chruser recently about this, actually. I was saying, we need to spread our human population out between more than one planet(same with our animals, if possible.) If something catastrophic were to happen to earth, our entire species would be wiped out. If we're split up between a few different places, it would still suck but it wouldn't be the end. Also, with more "bases", we would have more of a chance to eliminate any potential threats(such as meteors and shit like that.)

As for the morality, I don't really see how there would be any problem with it. I mean, if there was some sentient lifeform that we were wiping out, I'd see a possible problem with it(and also possible provoking some problems farther down the road, depending on how intelligent they are.) Wiping out a bunch of bacteria doesn't seem like a big deal to me.

So I say, for cases such as mars and venus where there's not much if any life (I don't know much about the ecosystems of either planet, if they even have ecosystems,) let's terraform, baby!