Most people are easy to manipulate, religious or not.

1. Why do you think fake news are a thing? People are willing to believe whatever will suit their narrative without actually doing the (real/hard) work of cross-referencing and checking said news (edit: aka, without using their brains). More importantly without ever daring criticize their own beliefs—aka the ‘we’re right/we’re the good guys’ vs the ‘they’re the wrong/the bad guys’ type of discourses that seem to prevail in our (manipulative and manipulated) societies.
2. What could explain those almost instantaneous gathering of large crowds based on anger or fear? Most people are willing to use anything as a pretext to let their anger/fear free to express itself and wreck havoc (back to point 1)

People being religious just tells us the type of things they’re more likely willing to believe in/act upon. But the gullibility is the same with or without religion (edit: and that is real major issue in everything that’s going wrong nowadays), to me at least.