"Don't want the GM to be able to flat out kill your character? Join a game where that is toggled off. Don't want the GM to be able to help you? Join a game where that is toggled off. Don't want the GM to be able to etc.? Join a game where that is toggled off."
Why would any of this matter? This is someone GMing a game you are in, your character is for their game.
I agree. If you join a game with a GM who has terrible ability or is a troll, having a couple flags like this are going to be meaningless.
Imagine a troll joins a random session as a player and immediately starts killing everything in sight.
We just can't force good behaviour with mechanics like this. A rating system might work, or even just some kind of forum where you can meet people. I think the latter is preferable, because roleplaying is generally a commitment you make for more than just one afternoon.