We all know they’re not going up there for the good of humanity or whatever. They want to turn their billions into trillions.

Yes, and necessarily figure out and establish lunar industrialization in the process. Depending on viewpoint, this can be a big argument in favor of the good of humanity.

I agree we need to fix our economic incentives and inequalities.

Though I don't see how the Moon of all things should be spared from capitalist exploitation. It's probably the one place where they can't do much harm, no matter how hard they capitalist.

Theses worries are fully justified when it comes to rain forests, deep sea mining, child slavery, union busting and pretty much anything they touch on Earth. But on the Moon?

There is one interesting worst case scenario: A corporate monopoly exploits the Moon so ruthlessly, that it outcompetes terrestial production. Let's say certain building materials or other things of value are suddenly much cheaper to import from the Moon than they are to make on Earth. Wouldn't that end exploitation of people and animals in these industries on Earth, preserve ecosystems which would have been destroyed otherwise?

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).