In a perfect world, the relationship between private opinion and public opinion would be basically like a mirror. At its best, the public opinion holds a mirror to us, and it reflects exactly who we are. But because of collective illusions, that’s typically not the case.
Collective illusions lead individuals to make decisions that are contrary to their private values simply because a majority of people in a group believe the majority thinks something that they don’t. As a result, the entire group can end up doing something that almost nobody wants, which is fatal to a free society.
But if society creates a space where people feel comfortable expressing views they believe might deviate from the group, you’ll find out pretty quickly whether your impression of the group is correct or not. Even when we fundamentally end up disagreeing, a truthful disagreement is always better than a collective illusion.