What makes you so sure that we won't be able to? If associated with religions, does your religion not believe that we are able to accomplish it?
NASA has been working on a new project to send a Men to the Moon, and even Mars. It will be decades before it will be operational but it's more than possible to settle on a different planet. That's the difference is unless we fly to the Earth alike planet lightyears away, and say settle on Mars, the only life supply would be transport ships sending supplies to and from Mars, or the moon, or wherever we'd land.
If I would've had a religion, I'm pretty sure one could argue that leaving earth is a sin. God created the earth for us, so when we seek to leave earth, aren't we then leaving behind God as well?
I was trying to say that extraterrestrial human settlements are very, very unlikely to happen. Even though we can send men to the Moon, maybe even to Mars, we aren't able to build lifesupporting colonies there. And going beyond our solar system? Forget about it. The technological challenges are way too large. Not to mention that the journey itself would take hundreds or thousands of generations.
Let's face it: humanity is bound to earth. We only have a relatively "short" time left, and there's no way we're going to settle on a different planet during that time. Therefore, we should spend our time and ressources to live as sustainable as possible.
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