To clarify and sum up: It mainly needs to avoid the implication that "only a total moron would believe such a thing". Because that implication leads directly to the person who *does* believe such a thing - if they're alert and intelligent enough to follow the obvious logical* chain - reacting exactly as if you had just outright called them a moron. Because to all intents and purposes, you did.


EDIT: Correcting myself, I don't mean logical chain, I mean *inferential* chain.

At bottom, what we're talking about is avoiding triggering unhelpful/negative emotional reactions, unless one has good cause to do so.