The parent never said smart people couldn't hold completely irrational beliefs. They just did not arrive to their position by reasoning about the issue.
I was reading this article about a vocal Japanese revisionist. Like creationists, or conspiracy theorists, there is nothing rational about these beliefs. When you reach for the conclusion first, and establish it is the absolute truth and then cherry-pick and twist facts and make excuses to support your conclusion, you are actively engaged in a process of denying reality. These people don't need a TV debate, they need a therapy.
On the other hand, you probably have people who have never really examined why they believe in creationism, and do not suffer from the same disease. These people may be convinced, perhaps, but they are not the ones at the frontline of the movement, frothing at the mouth and being engaged in a public debate as if they had any shred of credibility.
> Even smart people believe dumb things because they have a greater ability to rationalize their choice of beliefs.
This is quite true -- many very smart people hold onto embarrassing beliefs only because they can (and do) out-argue anyone in their immediate environment. There's a name for this that I have unfortunately forgotten.