No-one on here knows everything about everyone. We only know what people post, and sometimes that is not true. Anyone can post anything!
But in the outside world, anyone can tell you anything, too. It is easier when you are face to face to see when someone is not being completely frank.
On here, you just have to go by all the posts you have previously read from someone. If they contradict themselves, you start to wonder whether they are making some of it up - but sometimes people DO think differently from time to time.
I can only speak for myself, but I can assure you I am not a member of any dangerous or extremist organisation. I have met quite a few other posters, and I don't believe any of them are either. Thatbags certainly is not, in spite of your fear of her atheism - but that is not catching!