I think the notion of gray Jedi can work – if such characters are clearly portrayed as antiheroes/antivillains with questionable morality.
If that’s a temporary state. Eventually you should have to pick a side, because that’s how the dark side works. Usually these characters exist for video game purposes, literally just because force lightning is cool and you want to be able to use it without being evil. That’s fine for a video game, but when people try to start using that concept to make statements about philosophy in universe or in real life, it’s ridiculous.
It certainly shouldn’t be something done on an organized scale or used as the ideal.
I don’t like any of the Legacy stuff but I think something like the Imperial Knights would be a good exception. They use the Force as part of a specific political institution, a cause that’s higher than themselves but not truly good either. Which is different from the normal “gray” concept of just using whatever you feel like because it works better for you personally, and getting away with it because you’re just better than everyone else.