What you moderators could do is to intervene - as moderators - in debates and ask people who fail to provide source references to do so. Too often, discussions degenerate because some people take advantage of how easy it is to get away with totally unsupported assertions. I can understand Don Caldwell's feelings toward long threads - sooner or later many of them degenerate into loose assertions, and those who contribute with supported facts withdraw, leaving the scene to the babblers who have no reliable sources for their assertions.
You could intervene in threads with written warnings: "Show your sources in your next post, or it will be deleted. Such unsupported assertions lead us nowhere."
If you force people to shape up in that way, I'm sure we will be saved from much unnecessary mudslinging, and it will create a much better culture on this board. There is a Swedish saying - the first to raise his voice is the one who feels that his position is weak. (Maybe typical of us calm and boring Swedes
)
All best from an ice cold Sweden,
Christer Bergström