Mentoring should have a higher standard because people volunteer for it, you don't "earn" it. You are agreeing to being a guide and coach and a teaching position requires patience and understanding most gamers don't have. If you are proven not to have it, you don't need to be a mentor.
This is why I also said it should be reviewed just like a normal report. It shouldn't just be "tick tick tick too many reports you lose mentor". Enough people report you for bad mentoring someone takes a look at the logs and makes a call.
As mentioned in my post , hence the edit, by review. GMs will have standards to follow.