Why do people feel the need to pick apart research studies?

I have been known to post the findings of research studies in non-science communities (such as this one) because discussing the findings of the study and their implications would be interesting. But inevitably, the discussion tends to be about potential mistakes in the study design.

If these criticisms were valid and meaningful, then isn’t it safe to assume the authors of the study—who spent months, if not years working on it, and are experts in the field—would probably have thought of them first? If not them, then the reviewers (also experts in the field!) who had to approve the study for publication?

This is not to say that all research studies are without flaws. But the flaws that exist tend to be not immediately apparent to people who are not educated in the field and do not have a good technical understanding of statistics.

So: is this impulse to pick apart research studies hubris? Reflective of a general distrust of science and scientists? Or can it be explained away more innocuously?