I think the need for most people to assign the label “crackpot” vs “credible” almost immediately to any claim (especially to the more far-out claims) is an aspect of human nature: a desire to break down and simplify our view of the world into discrete categories as early as possible.

I think we do this not because this is the most accurate way to think, but because our minds are finite, and we need some simplifying approximation (e.g. quantization of a continuum into categories, or binary decisions) in order to make thinking about the immensely complicated world even possible.

For example, we tend to seek conclusions like “we have decided that A is good, B is bad, C is bunk, and D is science — case closed!” When in reality, our understanding of truth is far more a continuous and constantly evolving thing, as new information and ideas flow through.

Put simply, I think most people are just uncomfortable answering important questions with “I don’t know”, and avoid that answer at all costs, even when it is the correct answer.