If there are well-meaning people who are honestly investigating the evidence and drawing conclusions that differ from mine, then I do not automatically label that "stupidity."
I think that someone refusing to investigate evidence or saying that some evidence is off-limits or some possibilities are off-limits is a much bigger problem than someone honestly looking at all the evidence and then reaching a different conclusion from the main stream conclusion.
So, there may be well-meaning people who honestly look at the evidence and find themselves believing flat-earth arguments, and I'm not going to call them names.
In fact, I am offering the above evidence and reasoning for those well-meaning people who may be interested in looking at the evidence that (to me) is extremely conclusive. The sudden flurry of very vocal flat-earth web activity may have caused some honest and well-meaning people to have their doubts, so I am offering what (to me) seems to evidence that makes it beyond doubt.
What I suspect your question is really about, however, is people who are not necessarily honest or well-meaning in their strident pushing of this issue as a way of side-tracking discussions. Obviously, I believe that a lot of this sudden and very vocal flat-earth activity on the web may well be in that camp.
Some of the reasons to suspect that is the very sudden appearance of people who are actively seeking out places to add flat-earth comments, even if the discussion had little or nothing to do with that subject before they showed up, and the very frequent use of derogatory and inflammatory language and name-calling -- both tactics that seem to be calculated to disrupt honest and open conversation or the sincere search for the truth.
If there are people who are aggressively seeking to disrupt other conversations in this way (which seems to be pretty evident), you would have to ask them yourself as to why they would do that -- I can't shed any definitive light on that subject, and I have not spent any time investigating it.
Sophists have been around for a long time, judging by the conversations in the works of Cicero and Plato and others.
Perhaps some people just like to argue positions they don't actually believe just for fun, or disrupt things just to be disruptive.
But there are also plenty of other reasons beyond "just for the fun of it" that people might want to disrupt certain discussions. I would guess that the people who honestly believe the flat-earth position and who may have believed it for years are probably not the same ones who suddenly in the past twelve to fifteen months suddenly started becoming very disruptive and intrusive and insulting / hostile with their views and comments.
I think that people who have been writing about alternative theories for many years, and who have been writing about the problems with the "conventional storyline" for many years, can attest to the fact that four or five years ago, conversations were not constantly being interrupted by long streams of people arguing back and forth about the shape of the earth. I haven't been writing about these subjects for as long as many others have, but I have been doing it long enough to say that from my personal experience this is a very sudden phenomenon.
To finish on a general note, let me say this. A characteristic that can be seen in the phenomenon we are discussing might be framed in general terms like this:
* an aggressive commentator says that everyone must believe "X position"
* the commentator categorically states that anyone who does not agree with "X position" is lying to you, or is morally defective, etc.
* anyone saying that "X position" is not proven and we should honestly look at the evidence, because it seems to suggest possibilities such as "Y" or "Z" or "R," is similarly insulted,
* Possibilities such as "Y" or "Z" or "R" are declared to be completely beyond the pale and no one should ever even think about them or consider them.
We can clearly see this behavior going on with aggressive flat-earth commentators.
But where else and about what other subjects can we see this same pattern manifesting itself?
What other "possibilities Y, Z, or R" are declared to be off-limits for investigation or even consideration?
What other name-calling is leveled at those who propose to honestly consider evidence that seems to point to possibilities Y, Z, or R?