Bertrand Russell once listed a series of guidelines for intellectual integrity. I'd like to discuss them all at length, but I'll start with the top of the list: Do not feel absolutely certain of anything.
This is a view shared by Sir Karl Popper, the godfather of falsifiability. His stance was that any position we take should always be regarded as tentative. But he also made it clear that the further we go, the more work would be required to overturn an existing position. It was far easier to unseat the Ptolemaic or geocentric view of the universe than to unseat the Einsteinian view of the universe, in big part because each unseating builds on the successes and learns from the failures of the prior one. Unseating Einstein would take more effort than I am capable of visualizing, but I'm one man and I'm not even a physicist. The door has to remain open. But not just so that any old thing can walk through.
Where this view becomes abused is when people use skepticism as a self- or other-directed weapon.
The former, where you doubt yourself terminally, is not skeptical thinking but paralysis or indecision, the unwillingness to commit to a course of action or thought because of perceived fears about the cost of failure. (The perceived cost of failure is often drastically out of line with the actual cost of failure, while the very real cost of inaction or paralysis goes unnoticed.)
The latter is when "skepticism" is sown as a weaponization of discourse — e.g., the Sandy Hook victims were "crisis actors"; there is "no proof" the earth is actually round, etc. This isn't skepticism. This is an attack on the idea of discourse itself. The point with sowing such discord is not to encourage a lively dissent, but to make real discussion impossible, to shut it down and make any search for truth pre-emptively pointless.
The determinant for whether or not such things are an attack on discourse should not be "How outrageous is this idea?", but "What are the standards and evidence being invoked to support it?" If it's impossible to disprove the idea, or if the goalposts for same are constantly being shuffled around, or if the standard of evidence invoked is unsupportable, or if the sources and evidence are worthless, those all point to the weaponization of the discourse. If someone wants to believe there were no Sandy Hook victims, then no actual thinking or discussion is taking place; it's just an invocation of their need to believe something to satisfy whatever emotional chimera they have. As I'm fond of saying, they weren't argued into such a thing to begin with, so there's no point in trying to argue them out of it. (It might be possible to do that in a different, more intimate venue, where it's just you and the other guy, but that's another issue.)
The point of maintaining skepticism about things is not to cloak everything in a fog of hopeless doubt. It's to maintain at all times criteria for what a valid challenge to an idea would consist of, whether for one's self or others, but mainly for one's self.
The most important thing to remember, though, is how even the most enlightened of discourse takes place in the real world. Some people don't want to have a discussion. They want to win at any cost, including the possibility of ever having another discussion. And because they know on some level their ideas won't survive scrutiny (or just don't care), they use the default tolerances of an open society against its inhabitants. Removing such people from the discussion is not a violation of the principles of free thought; it's one of the few ways to guarantee the continued existence of such principles.
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