First, I think that religion is an opinion like any other. As so, you may subject it to the test of reason, and religion always fails this test, because it's in its nature to be based on faith : believing without proof. Even the most elaborate theological theories are in the end based on faith. So, for me, someone who bases his belief system on something irrational makes a dumb decision. It's dumb like having a political opinion and not knowing why.
It doesn't mean that the believers are wrong, because there may be a God or a supreme being of some sort, but you can't deduce the attributes of this Supreme Being nor his very existence from anything rational. So why being Muslim, Christian or something else ? It's irrational, and it's greatly because of education. If you've never been told about a guy named Jesus, there is zero chance that you become a Christian, which is inconsistent with the idea of a divine revelation.
But do respect believers. I don't think I'm immune to make dumb decisions, but most religious people deeply think that people like me are inherently inferior because of our lack of faith, and that all the bad things that may happen to us are well deserved. So calling a believer dumb is not worse than being called a bad people because you don't believe.
Moreover, it's true that if you lack the will, or don't have enough reasons to keep yourself away from drugs, stealing, or any behavior that is antisocial, the fear of a divine retribution may be useful for society. I don't if it's better or not than having a strong system of moral values based on respect of other human beings. It's an endless debate to try to figure out what good, if any, religions made to humanity (inquisition and crusades versus peace and truce of god). After all, strictly godless societies were nightmares (think about the Nazis or the Communists).
So, maybe it's better to be dumb, because we don't have very good results to show when we try too hard to think by ourselves.