Background: There's this effect when you have some idea, i.e. that eating other people is (probably) cool, you join the group of like minded people, you talk about how tasty people are, everyone agrees with you, which reinforces the idea, and you all share literature and articles and youtube videos and whatnot on how cool it is, and the longer you all participate in the people eating community the more sure you are that it's cool because of all the friend confirmation and the info you see and share and so on reinforces the belief stronger and stronger, and you don't meet people with opposite ideas that often, don't read criticism on eating people that often, etc. And the people eating idea is no longer just probably cool to you, you become sure about it with all your heart and defend it fanatically.
I am pretty sure I've read about this in some Peter L. Berger's book, however I cannot find it.
What is the name of this effect? (i.e., whereby being part of a group strengthens your belief in the beliefs held by the group)