I took my wife and 2 of our gym climbing buddies out to Smith for a weekend. None of the 3 of them had ever climbed outdoors before and were slightly nervous about safety. After watching many of the other climbing groups around us, they were VERY confident in their own technique and mine. It pains me to see friends 'teaching' friends to belay improperly, but it seems to be a common practice.
An old saying goes, "it takes a village to raise a child." I feel similarly about climbers. I personally think it's a good thing to point out bad scenarios to others and to help them see the errors of their ways, as long as I'm staying firm but peaceful while doing so.
Two words you don't want to hear around you while on belay:
ROCK FIGHT!!!