Throwing invalid and in many cases demonstrably false claims at students who don't have the background to see the invalidity is ludicrous.
But the real world throws-out false and misleading claims all the time. If we don't teach students how to think critically, how to weigh evidence-backed claims against claims based solely on authority, culture, religion, etc., than how are students ever supposed to gain the skills required to make reasoned choices when encountering conflicting 'facts' for the first time?
I mean, why single science out? Why not teach Holocaust denial in history class? After all, wouldn't that challenge students too? Perhaps you could also teach 2+2=5 and French verb conjugation in English class.
I dearly hope schools teach Holocaust denial in history class, and the conjugation of French verbs in English class. Examining the reasons why Holocaust denial persists against overwhelming evidence to the contrary can teach far more about why the Holocaust happened in the first place than any mere regurgitation of the historical facts involved. In the same vein, comparing and contrasting English verb conjugation against the French equivalent can serve as a stepping-stone to understanding how language actually works, which can in turn lead to a whole host of fascinating ideas you might never have even imagined existed otherwise. So yes -- I do hope schools are teaching exactly these kinds of things.
Schools are supposed to teach science, like any other subject, to a reasonable degree of accuracy. Teaching students that somehow just because someone calls some nonsense claim a "theory" is not teaching at all.
You're talking about teaching science instead of religion in the classroom; what I'm suggesting is that we'd be better off if we simply taught the scientific method instead. Ultimately, I don't believe that science lies only in facts like the weight of an electron, or the density of water at one atmosphere, or concepts like the Theory of Evolution. At least as I understand it, what science is truly about is a way of looking at the world around us, thinking about how that world is actually put together, and then testing those thoughts to see if there's any evidence to support them. I think if you can teach core concepts like that to students, and get them to understand what it really means, than you'll have armored those students against the myriad of dogmatic 'truths' the world is all too likely to throw at them.