I normally quest as a Healer but that's because I'm normally too lazy to swap to my offspec or am in LFD pretty much all the time, I get groups so often that swapping specs is pointless.
Once upon a time, questing in tank spec was slow, grueling and a clear sign of someone that had no idea certain trees were for pvp or leveling or end-game. This hasn't been the case since tank damage was somewhat normalized. In fact, I recommend leveling as a prot warrior for sure nowadays. Pulling big groups is the way to go if you're glyphed properly no matter what class. Plus, random dungeon queues are far more tolerable when you're queuing up as a tank.
Nope, not at all. Sure it isn't as fast as a DPS spec when it comes to killing stuff. but i've already got my main to 85, so i'm in no rush, and i like the fact that it'll take an act of divine intervention to make me die and have to do a corpse run.
Of course, maybe that just makes us both weird, but normal is boring.