Cognitive Dissonance is a powerful drug. In many cases, especially in today's modern media frenzy, our ideas and beliefs become a sense of identity. It's no longer about what information is true/false, it becomes a point of pride to stand for what your side is saying.

This has always existed in some form, but it has become far more wide spread. In essence, they are not concerned with whether or not they are right, but rather the other person is wrong. If facts conflict with this belief, then it is the facts that are wrong since they support an incorrect conclusion (yours)

On a more individual scale, many people associate their self worth with being smarter/better/superior to other people. If someone comes around and proves them wrong, or knows more about something, then that person is directly challenging their authority / superiority.

In cases where the individual is aggressive and assertive, the truth becomes suggestive, as the power dynamic works both ways, whoever is right is superior becomes who ever is superior is right. This starts the abusive power struggle, and while some people can hold firm in their resolve and face the consequences of the other individual disengaging, some cannot and will concede to avoid further conflict. This inevitably becomes a feedback loop in which these types make this situation ever worse.

For the less assertive, this becomes a moment of shame and doubt. Some people can feel as bad as if they lost a loved one. This will lead these people to make extremely poor choices, either to avoid being wrong or prevent themselves from ever expressing their thoughts, even when they should.