We do indeed need good Game Masters. We should absolutely not design a game system to protect players from bad Game Masters. Every rule written should be as desirable for a good Game Master as it is for a bad one. It is ok for rules to be optional and to exist from game to game based on player interests and desires. Rules for variety and flavor are not in question here. Rules that exist because it is believed they can rein in a bad Game Master are bad and harmful to the game.
So what is a good Game Master? A good Game Master is someone who is devoted to the fun of his group. This one trait and the will to learn is all it will take to be a good Game Master. He has his creativity and his energy to offer to provide a campaign that his players will enjoy. A good Game Master will know his own strengths and weaknesses and seek out players whose interests resonate with his own. A good Game Master should want to learn and to get better. He should be flexible when possible and strong when not. He should make sure that all players are having fun including himself. A Game Master has to always realize he can make a mistake and he is allowed to fix it and learn from it.
A good Game Master can be unskilled. You can pick up the game for the first time and be a good Game Master. Your intent will triumph ultimately. You will make mistakes when you first start. You will also make mistakes when you've been at it for thirty years. Hopefully not as many. If your players have faith that you are in fairness striving for the game to be fun and trying hard to be fair, they will be understanding. There should never be enmity or rivalry between the Game Master and the players. If you have players that don't respect your efforts and can't accept your work as an unbiased gift of fun then you should find some new players. Not every Game Master is good for every group of players. When a Game Master finds a group that he can have fun with then he is fulfilling his mission. The mission is fun.
A bad Game Master is someone not devoted to fun for the entire group. His own fun is all that matters and ruining others fun is fine so long as his own is not lessened. If such GM's acquire any skill it is only in grieving their players and causing them to curse the game. I've met a few lost souls along the way who've been abused by such Game Masters. These kinds of people do not help the game and are better off out of it. They should either be confronted and forced to reform by their players or they should be ousted as Game Master.
The game designers will fail to protect a group of players from their Game Master. Rules designed to prevent abusive Game Masters are wasted space. Game Masters can change anything. They can create any circumstance. They are unstoppable by rules. Rule 0, the best rule in the book by the way if used benevolently, is impossible to resist if used for harm. So protecting players from their Game Masters is a fools errand.
Instead the game designers should focus on helping good Game Masters to become more skilled. Help those Game Masters, who want to make their players happy, be more effective at doing so. The Game Masters guide should absolutely tell Game Masters that they can change anything at any time in the name of fun. There is no wrong way to role-play using the rules. If you use them to have fun then you are winning. So I call out to the games designers to know the difference. Know that good Game Masters want help and bad one's aren't listening anyway. Give us clear rules that are easy to use and easy to adjudicate because good Game Masters still need help. Help good Game Masters to avoid mistakes and continually improve.
When the game designers spend time lessening the fun for good Game Masters and their groups in a vain attempt to make bad Game Masters behave is a wasted day. There is no right way. There are only many disparate fun ways for many disparate groups. Help those groups and their Game Master to prosper and have fun and they will not forget you.