"One of the saddest lessons of history is this: If we’ve been bamboozled long enough, we tend to reject any evidence of the bamboozle. We’re no longer interested in finding out the truth. The bamboozle has captured us. It’s simply too painful to acknowledge, even to ourselves, that we’ve been taken. Once you give a charlatan power over you, you almost never get it back.” – Carl Sagan.
Above: The late rebbe of Chabad-Lubavitch Rabbi Menachem Mendel Schneerson
If you want to know why Carl Sagan said this, and why many people say it with regard to religion, read When Prophecy Fails: A Social and Psychological Study of a Modern Group that Predicted the Destruction of the World by Leon Festinger. You can get the Kindle version for 99 cents, and the Kindle app, which works on Android and Mac phones and tablets or on your computer, is free.
If you read Festinger, you'll quickly understand the mass delusion that is today's Chabad-Lubavitch and what was the mass delusion in previous generations of the entire hasidic movement.
For another Chabad example, at the moment when the third Chabad rebbe, the Tzemach Tzedek, died, his arguably least talented son – who went on to become the Rebbe Maharash over the opposition of almost all of the Schneersohn family and after a long beit din [Orthodox religious court] fight, called out something to the effect of, "he's still here with us! he will still answer our prayers!" The Maharash then built his life around living off the donations of hasidim who came from across White Russia to visit the Tzemach Tzedek's grave. The Maharash drove around the town of Lubavitch in a golden carriage with a large entourage, wore gold embroidered clothes, and fancied – and ate – copious amounts of gourmet food. His followers were primarily hasidim who believed the Maharash was in communication with their dead rebbe – the same delusion that fueled modern day Chabad-Lubavitch for decades. Most of the hasidim of the Tzemach Tzedek left the Lubavitch branch and followed other Chabad rebbes, the brothers and nephews of the Maharash. In the modern day iteration, there was no other Chabad rebbe to follow.
At any rate, if you want to read about how this type of delusion takes hold and how cognitive dissonance fuels it, read Festinger.
[Hat Tips: Audrey the Liberal (for the Carl Sagan quote); Mark S. (for Festinger).]