You are quite correct that the appropriate place for some disagreements is off the boards. Flames and their inevitable escalations invariably take away from the overall quality of a public forum such as this. There are many well thought out opinions, genuine good ideas, and a wealth of practical information directly related to game play.
In short, this is among the best forums of its type on the web today, and it is due entirely to the efforts of the people who populate it, and the people who police it. It must be a very difficult thing to moderate the differences of opinion that exist among people of such varied ages and backgrounds as those that use these boards.
I think that the person who contacted you via PM probably would not be the kind of person that WOULD engage in public flame war. That sort of thing requires a level of maturity that most flamers lack.
Having said that, however, I think that there may be situations where a public flaming CAN be beneficial.
In the case of an individual who is consistently antagonistic, degrading, unsportsmanlike, immature, and just plain mean, a public butt-kicking may be of benefit. Not to the individual in question, because they are likely too immature to understand what has happened, but to those who continually observe their behaviour and are the targets of it. (read "yaaay")
I don't for a minute think that this thread was directed at me, although I notice that a certain thread containing a MONDO flaming has been deleted.
I just think that it is important to consider that some people just damn well DESERVE it, though perhaps not nearly as many as actually participate in these things.
Actually, now that I think about it, maybe the mods DID consider that. I haven't heard anything about it since it was deleted, so maybe they have a sense of justice after all.
Maybe we could have a "FLAMEWAR" forum that the mods could move certain posts to when they see a disagreement escalating. That way, it could still be fun for the spectators, the aggressors could have it out, and it would keep the legitimate discussions clean.
Many flames are also really funny, so maybe the day will come when we could also have awards for best flames.
We should take comfort in the fact that nearly all of the people that post here are mature, tolerant and willing to consider other viewpoints when a discussion arises. I have seen very little evidence of true flame wars since I have been reading these forums (since 2004 I think).
Finally, if the person who sent you that PM was correct, and you do consistently critique the efforts of others, without making or having made similar efforts yourself, then it WOULD have been appropriate to bring that up in the public forums. Everyone here has nothing to guage the value of your opinion on, except whatever information they can glean about you here.