You pose a very interesting and thought-provoking premise to question everything and not just accept it. This I believe to be the heart of philosophy to seek truth and understanding. It is true we naturally and for the vast majority of us we take and make academic/ mental shortcuts in our thinking. But surely that does not define us as either stupid or intelligent. I prefer to think that many of us for whatever reason we do not reason or think that deeply about all things. To do so would be endless. For many of us we hold values and opinions and beliefs on broader concepts such as fairness, equality, and love. It is from these that our thinking evolves and some of the examples you raise become easily solved.

Intelligence is multi-faced and subjective and for some people, they would argue the prejudice they hold is based on actual experience and consequential thinking. Which if that is all they know, you can understand their thinking. But it could be dangerous and wrong especially when it deviates beyond the broader concepts mentioned above.

The question for me which I think you are addressing is your degree of openness to discuss and interpret new and different ideas. Essentially how you choose to deal with cognitive dissonance, maybe?