If you plop a mining farm down next to an existing hydro dam that was previously used for powering aluminum smelting, then that farm is now funding the maintenance of that dam. That dam then can provide power to the surrounding community. It isn't about making up a difference, it is about keeping that dam running. Oh and what's worse for the environment then wasting energy on mining bitcoin? Aluminum smelting.
This is exactly what coinmint did at an old Alcoa facility in upstate NY. They are using power that would otherwise go to waste. It is too expensive to build more transmission lines to feed power to people further away. Re-using the Alcoa facility also helps fund its further cleanup from the years of toxic waste produced there. A bunch of drone computers is a perfect use.
I'm all for shutting down coal based mining. At this point most large mining operations are not profitable on that anyway and have moved to other sources of power.
Disclosure: I am a large very scale ETH miner who uses hydro (but not at coinmint, I'm just very familiar with their facility).