What would happen if somebody yelled "Freebird!" at your show, and you actually just played it? What would happen if EVERY musician decided to do it? Would it stop?

Yes, absolutely.

The bands would play the 14 minute version and the rest of the audience would stomp the living fuck out of the asshole who robbed them 14 minutes of their concert.

Good point, but I feel few bands can pull off Freebird properly. Also, 99% of people at shows go to hear the new cd and their old favorites played live.

hahaha. KMFCM, I *have* yelled "Slayer!"

Then again, I have also covered Slayer songs in a band which was most certainly NOT metal.