Stan's unorganized little thoughts:
Venus is too hot and there's no water. Jupiter is too hostile for any life and too far anyway. Mars is the only option to expand to, but it would take a year and a few months to get to with current tech, and it's a one-way trip with no resources on the other end.
Would unmanned craft need to be sent first to drop off some biological crap to turn Mars into another earth, then deplete its resources like here on earth? How long would everything take?
Mars is half the size of earth, it's too far, there are no resources there and clearly almost everybody will remain on earth even if/when we can get there easier.
Long, long, looooong, loooooooooong, before the sun becomes a red giant and possibly swallows earth, our planet won't be habitable anyway and the only escape would potentially be Mars, which won't be habitable either, because, sun...
That's all so, so, so incomprehensibly far away in the future, but still...
Humanity is doomed, even if in far, faaaar distant future, but my question is, wtf do we need to save our planet for? The inevitable is just that—inevitable. Are we just passing on the inevitable to the future us? "Haha fuck you, we managed to survive! You deal with this shit now!"