Nobody is stupid, nobody is deluded. (Or at least, nobody should be called these words in any conversation which is intended to persuade). However, this is not quite as nicey-nicey as it sounds because …
… some people are misinformed, misled, over-confident, mis-educated, or find themselves in miscellaneous other circumstances which cause them to be wrong in specific circumstances or on specific topics.
But nobody is stupid or foolish and it is counterproductive to say that they are (even if it makes you feel ever so clever to do so).
Are those who describe other people, in public fora, as “deluded”, “confused” or some other variation on “stupid” really interested in being heard by such people, in persuading them to consider alternatives?
Or, for that matter are they really interested in anyone listening in on the conversation being persuaded? An audience to this sort of shouty “you iz stooooopid” talk can go one of two ways. They can think “how rude, the person they’re shouting at must have upset them in some deep way, so perhaps the person being yelled at is right”. Or they can feel “hey! This guy is calling someone stupid, so it’s ok to be agressive in the service of certain opinions – in fact to ally myself with those opinions shows how smart I am – yippee I can be obnoxious with a good conscience”.
Side observation: robust language and hyperbole can be much less offensive in real life, and in printed media, than the same words used on the net. At least I can imagine situations where someone could say to me “sheesh – you’re talking complete crap” and I’d reply, fairly unconcernedly “oh Yeah? So come on then – what’s crap about it?”. But that sort of language really stings on the net – it’s enough to put me off entirely a lot of the time. Which suggests that there are people it puts off all of the time.