Technology

If we can replace the kind of mining that destroys the environment here on Earth with mining outside of Earth (not just the Moon, but maybe even more importantly asteroids on the Asteroid Belt) how is that a bad thing?

Even having Moon mining in addition to Earth-based mining will probably reduce the impact of the latter, if only by pushing down the prices of certain ores, making some Earth-based mining operations for those unprofitable and forcing them to close down (or never start in the first place) which will be good for people and good for Nature.

Or do you think the people doing the mining here on Earth (and more often than not leaving behind massive ecological damage) aren't "extracting massive amounts of profit" for doing it right here were they do a lot more damage?!

You really need to look at it in aggregate, not just consider only the first level effects and hence "more mining anywhere" = "bad" - "more mining way out there were it can't possibly harm people or Nature" is close to the best thing that could happen to our resource-intensive Economy (the best would be the end of Consumerism, but there are way more powerful moneyed interests align against it that against Moon mining).