Since 2 or more of you are arguing about impartial can you give examples of when you are not?
Speaking for myself I'm never intentionally not impartial. But since I'm creating the entire world, all the NPCs, hazards, obstacles and opportunities I am consciously or unconsciously influencing direction. Some of that is intentional because I don't care for murder-hobo dungeon crawling so we talk about that in our session 0. There are certain borders to my sandbox, if you want to take over the local mafia and run a criminal racket I'm not the right GM for you. I guess that would be the simplest example that some people would call not being impartial.