In his book Kindly Inquisitors, Jonathan Rauch makes a defense of science, free speech, and skepticism. Rauch summarizes the essential principle of skepticism: "We must all take seriously the idea that any one of us, and all of us, could, at any time, be wrong."
No one is above scrutiny and neither is any belief. A corollary of this principle is that honest criticism is always legitimate. If any belief can be wrong, no one can legitimately claim that the discussion is over, ever. In other words, no one has the last word.
Sounds good, but...?
But if this is correct, the discussions have to go on forever, which is exactly what a lot of science deniers try to achieve (think of anti-vaxxers or climate change deniers). Another voice, another opinion... on and on ... ad nauseam...
Maybe even if no single person can have the last word, the scientific community can have it when a point is reached where no reasonable doubt is left.
"Measles is caused by viruses, not bacteria". Period. No further discussion is needed or useful. - Or: "man-made climate change is real. Period".
Why is anyone excluded from the science community?
Yes very true. There are two extremes to avoid. Absolutism, the belief that you have found, or been given, final truth on everything, which brings with it bigotry and dogma. And. Relativism, the view that there is no final truth, which brings with it apathy and is anti-progress or improvement.
Between those two extremes is the belief the perfectly true things may exist, but that you are rarely going to have them, and that therefore research and life, are the business of trying to get closer to the final truth, as a target and aspiration rather than a destination. But that does not mean that all ideas are equal, because it follows from that, however, that those who have done the most work, with the most discipline, attention to detail, elimination of personal preferences etc. are 'likely' but not certain to be the closest to a final truth, and therefore have the ideas most to be trusted.
Unfortunately those who most need to understand the Dunning-Kruger Effect are the least likely to grasp it. So anti-vaxxers who are wholly unaware of statistics and biology potificate on their own sublime brilliance.
The same can be said for pro-covid-19vaxxers, you see that also? Pretty good at ignoring statistics which strongly suggest transmission is not being stopped ie not going to achieve a herd immunity with these medicines so what is the justification for coercion and removing consent for a medicine that just protects the individual?