You assess the facts and make your (informed) opinion. You defend that opinion because it's the best possible opinion, i.e. the most truthful. If the facts change, you re-assess and re-form your opinion. You are loyal to the "truth", not a belief. Or your ego.

As somebody slightly on the autistic spectrum, I find it hard to understand why a lot of people don't operate like this.

There is of course a difference between factual information and emotional response or differences in taste; I assume this discussion is only about empirical facts and not personal preference.