Let's face it, collectively, we're not as rational as we like to believe.
I mean one logical, rational argument used is that the universe and life is incredibly complicated, we as "mere" humans cannot create it, and it's incredibly unlikely humans would develop like we did. Therefore, there must be intelligent design behind it.
See? Rational and logical thought. Dismissing people who think differently as being irrational is just alienating and pushing them away, entrenching them even more if you go in with a judgment and mindset like that. It would make you scoff at "these people", because they're irrational unlike you, the epitome of rationality and logical thought.
TL;DR, assume the "other side" is just as smart and rational as you are, they just have different ideas.
Let me ask you: what would have to happen for you to rescind your belief?
Also; at the risk of starting a discussion about religion: you haven't developed a logical argument by saying "universe is complicated -> deity". You've only moved the problem of "who or what created X" up one level to the deity. Who created the deity?
Edit: Treating rationality as something real as opposed to just a (very useful) figment of our imagination, i.e. something like a variant of Platonic Realism, is no different from any other religion.
"economic man, is the portrayal of humans as agents who are consistently rational, narrowly self-interested, and who pursue their subjectively-defined ends optimally"