I've believed some very bizarre things in my life, by intention -- eg, once I decided to see if I could convince myself that alien life occupies earth and always has.* I succeeded, which is to say I came up with perfectly convincing ways to interpret even minor details of normal everyday life such that the presence of aliens was a better and more complete explanation of things that I took for granted with little or no explanation. It did not take long for me to consider my explanation as deduction, and that the aliens had revealed themselves to me. Very honestly, I lived with very little doubt in that state for months. I was not a kid either, that was in my early thirties. I still consider this an amazing period of time -- later on I managed to reindulge again, altho it did not last as long. It is a little exhausting, mentally, however, and can get in the way of thinking about more serious and important things. And, of course, it comes to dominate your emotional state and reactions to real events (for better or worse). But totally interesting to me, since up to that point I had always be a more or less scientific rational, athiethistic, WYSIWYG thinker.
I'm not saying that to belittle God or faith, I'm saying it because you are right Mario, I am sure plenty of sane, intelligent people really do believe in God and someone saying he does not exist will not change that.
However, one thing I do not believe is that this faith in a divine power can be extended so far as to make otherwise sane and intelligent people believe things like:
- slavery is okay
- blowing yourself up in a supermarket serves God
- women are not capable of higher thought
- everyone else's sexual practices should be subject to your scrutiny and interpreted in light of very convoluted revelations
These things are political, and in this case I would say either a) the person is lying and malicous, b) the person is indifferent and nihilistic, towing a line, c) the person is exceptionally stupid, or d) the person is not of sound mind and should not be considered a sane, rational adult.
* just thinking about it now I can't find any good reason (beyond occam's razor, which is in fact a very important rational principle) to not believe that.