Suggestible people follow instructions and (sometimes) take fewer risks. It is simply infeasible to logically convince people of every single thing that they ought to know. I hate to infantilize people in this way, but even the most capable and inquisitive minds among us cannot reasonably investigate everything.

People socially align over a lot of things, not just ideas. They develop shared tastes and preferences.

Even very undesirable characteristics such as sociopathy have a function in society. It is sometimes necessary to emotionally detach oneself from situations to make the right decisions. These are not good for every role, but they are primitive survival mechanisms and still have a useful function in keeping the peace.