chan rules:

Rule One. A group of people come to share a common view or belief that in some way is not properly based on reality.

Rule Two. Because their common view/belief cannot be subjected to external proof they have to reinforce its authority by claiming ‘consensus.’ The idea is to emphasize that all right-thinking people hold this view and that it is no longer open to challenge.

Rule Three: Anyone who disputes this ‘consensus’ must be excluded from the discussion: at best marginalized; at worst openly attacked or discredited.

See also: thegwpf.org/content/uploads/2018/02/Groupthink.pdf