The New World is so close to the Old that people had been visiting it for a thousand years before Columbus, some of them simply blown there in storms.

When they got there, there was air, water, and food for them, and a temperature above the freezing point of carbon dioxide.

Mars is humanity's best choice for another planet to live on, and yet it's a dark, freezing cold, airless, arid, lifeless, poisonous, radioactive desert.

There will never be a time when you will be able to step outside on Mars without protective gear. Terraforming would take centuries if not millennia and still leave the planet with an average temperature of about -70ºC. The very sands are poisonous!

The cost of setting up a self-sustaining Mars colony would be something like a quadrillion dollars. If you dispute that, try to figure out how much it would cost to get to the point you can make the first entirely Martian pressure suit, on Mars.

For perhaps 10% of that cost, we could save the living Earth, a planet which is already alive, has breathable air, water, and food.

"We can do both!" you say. We aren't actually doing either. Let's start by making some serious attempt to not kill our planet dead, and with it humanity, and then when that's under way, we can go back to outer space.