People are bad at maintaining the "I don't know" stance. But it's sometimes the only objective.
In politics "probable" is fuzzier concept and often just a cop out. You can justify anything with that idea, but you have no responsibility afterwards (damn, we went to the 5% range after all, sorry!). And you don't need any kind of real sources, just authority or lack of imagination suits just fine.
When we wander into personal world views or some casual conversations, assigning probabilities become really good idea. But then it's often about who's authority you trust most, than what data you can actually consider.
And end of the day most people still gravitate towards either "extremely likely" or "incredibly unlikely" most of the time. You just use likelihood as a way to show that you actually considered that your statement might be false, but you don't actually consider it to be.
This psychological tendency for people to make up their minds, and then not change their minds is actually at the heart of the problem. These "critics" could not have mass following to their bullshit ideas without it. But currently lots of people fail to understand that just providing half decent criticism against an idea does not prove the opposing idea true. Because human beings are naturally bad at not making their minds.