Roger: We know about the negative possibilities, but we’re just saying that the positives vastly outweigh them.
If someone makes a serious statement that becomes integral to an argument, why would they wantonly delete their time-consuming post? It seems like this would only be a problem for fickle, haphazard posters, whose posts wouldn’t make much of a difference anyways.
If it’s still such a worry, how about installing a Quote button next tot he Reply button, so that any response will carry the original statement in the same post?