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.

Exactly. I highly doubt raw iron or other common metals will ever make sense to import from space, but there will almost definitely be a market for materials to be used in space or manufactured in microgravity that can't be done on Earth.

Maybe, but habitats that far out probably never work because the sun is so weak.

why is the sun required for habitats.. plants can grow in artificial sunlight....

generational ships could spend entire decades in pockets with no sun...

all you need is the right raw materials, access to water and food, and fuel source to keep the uv lights working and the heater and oxygen pumping...

The energy source is the hard part. The sun will work for millions more years. Will fusion reactors work that long without some random failure of some part? Would you bet your life on it?

mirrors work forever in space

You don't need the sun when you have nuclear fusion.

or mirrors