Godwin's Law says, "As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches 1."  Since I started with the comparison, we can hopefully move forward :-) 

The reason I think the analogy is apt is that calling a truth claim "woo" is the least interesting choice the claimant could make.  If a claim is meritless, it should be easy to dismantle.  Further, it is important to dismantle it in as air-tight and a logical manner as possible so that those who would debunk the dangerous meme have artillery to do so and don't need to reinvent the argument from scratch.

Relatedly, calling a person a woo-monger is about as counterproductive as it gets.  If the intent is to convince them of the error of their ways, almost any other approach would be more effective.  If the intent is to convince the Greek chorus of sycophants (yours or theirs), then wouldn't any reasoned argument with any evidence be more effective?

My theory of woo-calling is that it's a sublimation of insecurity by the caller.