From the looks of it, there are two sides to this discussion.
Side one: Yeah! Life on mars is an advancement
Side two: Earth is crappy enough, why leave when we can fix?
.....
I think I'm on side one. If we don't leave, we would run out of room, recources, and earth would get waaay to mainstream. Also, about the europe analogy, nobody wanted to go out west because they didn't know what was there. Its human nature to be afraid of the unknown, but if Christopher Columbus (and every one else who explored) didn't have the balls to risk their life and go to America, we'd never even know about it. I know, Someone would eventually figure it out, but look how far back we would be in the understanding of our world if we had not have left then. Say we didnt find america until the 1800s. That would put America in the civil war, and we'd still think steam engines were the coolest thing ever. I'm not saying that would happen exactly, but its not far from the truth.
Now, I'm not saying we should jump into mars right away, but at least progress towards that. The moon is a good place to start, and then we could go to mars. But still, if we sit here trying to decide if we should leave or not, things will only gets worse.