Yes I listed believing 'a man died for mankind's sins' as a stupid belief. I don't believe there are 2 billion people in the world who believe this particular idea. Catholics are supposed to represent approx. 1 billion worldwide and the church counts a person catholic when they are baptized. In addition many people count themselves as part of a religious group when filling in forms but that doesn't mean they are practicing nor believe everything in that religion. For years, I'd count myself as protestant in questionnaires, depending on the purpose of the form. So I don't trust the 2 billion estimate. I think the particular belief "jesus died for mankind's sins" held would likely be by millions rather than a couple of billion. And of those millions ..yes Jason a high proportion of them would not be very bright. However that doesn't mean smart people are immune to holding stupid beliefs, so yes a percentage of those people would be highly intelligent and yet still hold that irrational belief. But on the whole I think true believers in religious nonsense...comprise mainly people, who don't think critically well
This site
http://www.religioustolerance.org/worldrel.htm states 33% of the worlds population is Christian, or about 2,039,000,000.
Of course it is impossible to tell how many really believe it and practice it. My guess is it is more then a mere millions. Maybe half? Maybe not. Even a quarter would be about 500 million. I work with a lot of Catholics. I would not say that they are died in the wool heavy duty practicing Catholics. But if asked if they believed in Jesus Christ as Savior I think most would say yes.
Now there is also a high percentage who have been indoctrinated from a young age and have never critically evaluated their beliefs, not because of stupidity but because they were never motivated to, perhaps exposed much to information which might motivate them to question. Those with above average intelligence on average are more likely over a life time to become educated and exposed to information which would lead them to critically evaluate their beliefs.
THey may critically evaluate them and still believe them, or part of them. This does not make them stupid or lacking critical thinking skills.
You write: "And what about Judaism that has a tradition fo God speaking to Prophets?" Every Jewish person I have met has been very rational Jason. They don't believe in man-gods. And I don't think many take the O.T. literally. Sure there are fundamentalist Jewish people but I think they are in the minority of Jews.
Most the Jewish people I know are Jewish by tradition rather than conservative or orthodox. Most I know don't really even practice it. One I know said to me in jest when expressing dissatisfaction with some of his tradition that he was probably the only anti Semite Semite in town. I did once work with an Orthodox Jewish woman. She was a true believer. My guess is a small part of the about 15 million Jews are Orthodox. I do not know enough about the other levels of Jewish practitioners to opine.