Re: we should leave Earth to survive
We definitely need to travel off planet in order to survive. We're one gigantic asteroid collision (or any other major apocalyptic event) away from dying off as a species. Life as a whole, if it is indeed currently confined to this planet, is at risk as well. Preserving life by spreading it across the galaxy may be the most important thing humanity will ever do.
I don't think this doomsday is coming any time soon, but it is coming. Best case scenario, we have until the sun runs out of fuel. So while we probably have a great many years to figure out space travel, it is a goal I never want to see people stop working towards. I don't care if it's expensive. It's necessary.