We all know confidently incorrect people. People displaying dunning-kruger. The majority of those people have low education and without someone giving them objectively true feedback on their opinions through their developmental years, they start to believe everything they think is true even without evidence.
Memorizing facts, dates, and formulas aren’t what necessarily makes someone intelligent. It’s the ability to second guess yourself and have an appropriate amount of confidence relative to your knowledge that is a sign of intelligence.
I could be wrong though.
Unfortunately this also gets abused by some people who believe they have a healthy level of skepticism, but actually are way off the deep end. Like anti-vaxxers, flat-Earthers, and other anti-science people.
So “healthy” in this context shouldn’t be defined by the individual.
Skepticism doesn’t necessarily entail outright rejection of something. Like, I could be sceptical about vaccines and their side effects, but still get the vaccine because it is the best option available to me right now.