Isn't it cheaper to mine resources in space for space travel then to eject them from earths orbit. If we found an astroid that had water that'd be worth it to b

Isn't it cheaper to mine resources in space for space travel then to eject them from earths orbit. If we found an astroid that had water that'd be worth it to bring it to a space dock or to any habitat that doesn't have water (planet, spaceship, satellite). I do agree the idea of bringing them back to Earth makes no sense, and the technology necessary to do that will probably make it not necessary thru other breakthroughs. But if you believe that Earth isn't the only location for humans to live we won't want to bring ML (Mega Liters) of water to future habitats, we want to either find it, or manufacture it.