Odhanan
Adventurer
I've seen friends have particularly bad experiences with bad GMs, but they were generally smart enough to realize these were not problems with GMs in general, but rather problems with the particular people GMing at the time. Therefore, I've never had some problem from someone else running a game carry over into my own game. The players at my table know they can trust me, and though there is a little bit of competitive teasing going on between the two sides of the GM screen, it's all in good spirit, for the fun of it.
tl;dr version: it's not a problem of GMing, it's a problem of people.
tl;dr version: it's not a problem of GMing, it's a problem of people.