"But there is *no* *rational* reason for their faith"

Of course there is a "rational reason" for beliefs that are mostly passed down from parents. For example, there are many many traditions and cultural beliefs that are passed down from generation to generation. Would one say that these are not rational? Of course not!

Asians use chop sticks, because their parents did. That's the rational reason they do it. I this use more "rational" than using forks and knives to eat? I suspect not.

Claiming that there is no "rational reason" to believe in something is a much different case than claiming that there is little evidence to support the belief.