The definition of atheist is someone who does not believe in God or deities. To them God is irrelevent by definition. Beyond that, atheism says nothing about having to be rational or capable of critical thinking. There is only a singular condition for membership. Conceptually, an atheist can do everything a religious person does, in terms of faith and dogmatic appeal and insistence, as long as it does not involve classic deities. It can involve human deities; idol worship.
Without classic Gods, which are above and therefore define what is right for humans, with atheists this is all done by humans who often appeal to the imagination.
The mistake theists make in arguing with atheist is assuming you are arguing with rational people. Even if most scientists are atheists not all atheists are scientists or b>>a. The vast majority are subject to all the conditions of religion minus the classic deities. You really need to approach them as people with relative religion without absolute deities; chance and chaos.