I don’t think religion makes people stupid, but I do think that unscrupulous people can easily abuse religion to manipulate gullible people for their own purposes.

Intelligent people aren’t swayed by dogma; they question it and are perfectly capable of recognizing when someone selectively picks out certain Bible passages (etc.)—or even makes them up—to push some position that isn’t further substantiated.

Stupid people, unfortunately, are not capable of this, which is why they are susceptible to manipulation—even when a religiously “legitimized” position stands in complete contradiction to the religious doctrine on which it is supposedly based. The best example of this is the fundamentalist Christians in the U.S.: Here, religion often serves to “justify” inhumane positions, since they serve the interests of the super-rich.

However, this often happens in such an absurd contradiction to, for example, the Christian commandment of love for one’s neighbor that it should be very obvious to anyone who claims to be a Christian. Since that is often not the case, however, the only conclusion that can be drawn is that the people who nevertheless allow themselves to be influenced by this are not believers at all, but merely idiots who parrot whatever a completely secular, false prophet feeds them—they are thus incapable of thinking for themselves, which is precisely what makes them idiots, and which in most cases is probably what led them to that “religion” in the first place, or rather, to the cult whose goals they allow themselves to be exploited for, against their own interests.

So no, I don’t think religion inherently makes people stupid—only when it prevents people, as part of their socialization, from learning to think for themselves and to evaluate and weigh arguments. This certainly happens in areas heavily influenced by fundamentalism, but it is less a problem of religion as such than a problem of its abuse by unscrupulous opportunists who exploit it for their own personal gain.

Every world religion serves a function in organizing society and teaches values for peaceful coexistence. Fundamentalists, however, abuse it to artificially create “in” and “out” groups, which in turn helps them advance their political agenda. Therefore, we must draw a distinction and consistently expose those opportunists who are motivated solely by their own self-interest: these include all fundamentalist movements that use religion as a means of political power - I don’t think there is anything religious about them, since their goal is always a political one.