It’s not group psychosis or mental illness, true, but it is divorced from reality. Sadly, the human mind is capable generating demonstrably, obviously erroneous beliefs without suffering from significantly abnormal psychology.

Religion is a set of extremely successful myths, which have survived mainly by convincing people that you can’t be a good person without them, which frequently involves disparaging people of other beliefs as bad/evil.

In other words, a really shitty worldview.