mbrooke I think you mean well but I also think your teaching methods may not be the best for a forum.
Insisting that a 50 Amp breaker is legal on #12 NM may be a hard concept for those will little electrical training to accept. Sometimes you can't shove an idea down people's throats just because you are right, you have to ease into it.
Did you ever consider haveing them go out to their own AC units and copy down the name plate data and explain it to you ?
It is safe to say I dont think you have experienced the environment on HI forums back then and I hope you do not ever encounter such. Believe me, we eased it, shoved it and everywhere in between when the other failed. We all tried our best with respect, pics, analogies, links, you name it. It was simply not a place for electricians no matter how good or well intended your teachings were. There was an "HI vs sparky" mentality. Electricians would routinely be ignored, called wrong, met with contempt and moderators would go as far as editing posts they did not agree with. Most would either leave or tension would boil over. Many highly respected and knowledgeable members like MDShunk for example were banned altogether at no fault of their own only because their posts while correct, contradicted what the other HIs were saying.
Of course today HI sites have gotten a lot better. HIs are listening, reading up on code, sparkies are coming back and some none HI professionals are even being offered memberships to their forums. Its getting better, no doubt about that, but back then it was a very different place.