Imperialism is wrong. Expansionism is perfectly fine. There’s nothing wrong with a nation or people improving their standard of living by gathering more resources and increasing their capabilities. It’s only wrong when that expansion is at the cost of other human beings or the environment.

I’m all in favor of space expansion. Maybe some day we can move our most polluting industries off the Earth’s surface. Hell, my dream would be a world where most people don’t even live on the planet itself. You want to live a big resource intensive life, the equivalent of modern suburban living? Do it in space. Want to do industrial agriculture? Do it in space. Want to run a giant factory? Do it in space. If you want to live on Earth, you have to abide by strict resource utilization and environmental impact rules. Everything else goes to space. The Earth becomes one big nature preserve with a few dense cities and organic farms scattered about.