Yes there are cases where they buy good power plants, but they also power from grid and buy dirty power plants. Even in case of good power, the investment should instead be made to make this power useful. Heck, folding at home or similar would be a hell of lot better usage.
But that isn't where we are. We're in a huge energy crunch, and having to go back on green policies because of it. During this time, ANY consumption is bad, and no, regardless of opinions on its usefulness, Bitcoin does not yet contribute in a meaningful enough way to sacrifice other utilities.
So yeah - I agree with you that we can waste power when and only when the vast majority of dirty power has been replaced.