I think we have to be realistic and appreciate that there will always be flare-ups on a list the size of this one. I can't think of many "clubs" of 700+ members where everyone loves everyone else and there are never any arguements or heated differences of opinion.
It isn't just restricted to old bikes either. If you look back at some of the old Royal Societies set up for various scientific or philosophical reasons, they were often at each other's throats-and they're supposed to be civilised!
When you bring together lots of people who are passionate about a subject, you will get friction. It's actually quite a healthy sign. The opposite, where dispassionate, intellectual, unemotional exchanges of information take place, sound great in theory but would probably fizzle out because they lack that vital spark.
As long as it doesn't get too nasty-and I don't think the latest exchange did-and both parties can get on with life and accept their differences, I can't see it causing any lasting problems. I think people on the list usually reach a point where they realise an arguement has gone far enough and it's time to back off.
If I were Dale, I'd sit back, assume the role of an omnipotent patriarch and just "tut, tut" quietly to myself until it blows over.