They have been indoctrinated to blindly follow an irrational dogma without question. This active discouragement of scrutiny is a symptom of insecurity which is a result of the total lack of evidence for, and the complete logical weakness of, the dogma. In the dictionary atheists are defined as people who do not believe in the existence of a god or gods. However in the vast majority of atheists the reasoning behind this disbelief in gods is rational logic. So most atheists are actually rationalists.
Rationalism leads to atheism.
Because science is the only logical, rational method of exploring and explaining nature and reality, anything that is not scientifically verifiable i.e. anything supernatural, is rejected as nonsense. There are thousands of god theories, most of them claiming to be the only true god theory, yet all of them are so logically flawed that they are ridiculously absurd. Atheists have concluded that the only true god theory is the no god, god theory. There is absolutely no evidence of a god or gods, or of any interaction of gods with this universe, so we see no reason for gods. If you believe in a god or gods, you believe in magic.