When lay people make definitive statements based on incomplete data, they're idiots. When "experts" do it, its lying. What they're lying about is the degree of certainty backing up their claims.

I used to work in the sciences and many PHD types have huge egos to the point where they are allergic to the words "I don't know." They'd rather lie than admit any gaps in their knowledge. The big ego types also tend to crave status and have the biggest mouths, so they often end up in undeserved decision making roles (Exhibit A: Fauci)