Same thing happens with the NPR, Science, The Economist, NatGeo, etc. groups on Facebook. You often can't have an intelligent conversation about a new science-related article without a gaggle of them redirecting the thread by interjecting some irrelevant or completely mistaken "point." You want to just leave it, but it's so insane or the actual facts so readily available, you feel like you have to respond, lest some unwary person take it seriously. You can let it stand which allows them to continue crowing about how nobody can refute them, or you can rebut their assertions which 1) feeds the conspiracy mentality (see! if we weren't on to something, why is everybody so MAD at us?); 2) makes them appear more legitimate than they are (see! people think we're worth responding to!); 3) doesn't prevent them from crowing victory no matter how inane their "point" is.
In rare and for the most part extreme circumstances, I have experienced both hallucination and delusion, but I realized the situation in short order. However the delusion some people have of their understanding of science is of an entirely different character.
This is, I suspect, largely due to the Dunning-Kruger effect.
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.64.2655&rep=rep1&type=pdf
