Believing that belief or non-belief in religion signifies any characteristic in people other than belief or non-belief in religion is silly.
To say that questioning the intelligence of Einstein regarding his stance on an "arbitrary" characteristic such as religiosity is silly, then turning around and calling everyone who believes in religion "weak-minded" is an example of cognitive dissonance. You take comfort that Einstein agrees with you and seek to defend him, but were Einstein to actually profess a belief in God, he'd just be "weak-minded" on the subject and thus his opinion would be irrelevant.
Personally, I see no direct connection between intelligence and religiosity. I do believe, however, that as education and cosmopolitanism increases, religiosity declines, as other ideas enter in, crowd out and out-compete religion in various spheres of knowledge.
The thing you've got to realize, however, is that the dividing line, if you so wish to demarcate one, isn't between believers and non-believers, but between those that understand that a degree of religiosity is just another aspect of a human being (which you seem to do when someone is an atheist) and those that feel it is a signifier of some inherent superiority or inferiority (which you seem to do when someone is religious).
“It is a strange paradox that today’s central banks are generally staffed by economists, who by and large profess a belief in a theory which says that their jobs are, at the best, unnecessary, and more likely wealth-destroying. Needless to say, this is not a point widely discussed among respectable economists. Nevertheless, it is an issue worth pondering.”
George Cooper, The Origin of Economic Crises