I think you could argue that this is an example of cognitive dissonance. It is uncomfortable to come face to face with new information that contradicts your beliefs or actions, and it requires energy if you want to integrate that new information into your worldview and adjust your actions. It is much easier to deny that information, even when it is clearly true.

For example, when it came out that aspartame might cause cancer, if you (like me) have eaten/drunk a lot of products containing it or have had a strong belief that it was completely safe, then it may be more comfortable for you to criticize WHO or think “well, it’s not really relevant for me because my family isn’t predisposed for cancer.” If you didn’t care about aspartame or artificial sweeteners before, you will probably readily accept that there may or may not be a cancer link.