As a cultural observation, how did the term "skeptic" morph into one who knee-jerk conclusively denies?
A skeptic is a person who questions the validity of something purportedto be factual. This necessarily implies investigating, considering, reasoning, learning; that is, curious enough to question and not just accept.
I'm not picking on you, Geoff. You are using the term as it commonly is used in modern parlance.
I think this misuse of the term is emblematic of our current intolerance of a discussion of ideas. For many people the other guy is either right or wrong - and you shouldn't listen to and can't learn from someone is "wrong." Unfortunate.