Why would anybody be afraid of something for which we have exactly 0 evidence for the existence of? Even according to RET civilizations are spaced so far apart that communication is essentially impossible (like, maybe one per galaxy, according to the most recent estimate I've seen). It seems a round Earth is rather positioned well to protect one from proof of alien existence too.
For the record I'm not afraid of dragons or babadooks either.
Interesting attempt at a deflection, at the end there. I certainly don't want to have the debate about what constitutes evidence with someone who says believe what you see for yourself... because how do I prove to you that I have seen what I have seen. So, even though I have seen aliens for myself (which again, according to flat Earthers, is the strongest evidence), I would actually refer you to any religious text... but specifically the Sumerian and Hindu histories (not just their recorded history, but their art, and their belief systems). If that is not enough for you, I also direct you to the fact that every known human culture has either believed in heavenly beings or people from the stars. But maybe that doesn't do it for you either, so try the impossible feats of architecture scattered throughout the ancient world, many of which we still wouldn't be able to reproduce today.
What I find most amusing however, are flat Earthers that dare say their believe is not based on either religion or a fear of extraterrestrials (in my opinion, the same thing)... because your suggestion, is that we exist on a magical plane of existence (where water doesn't simply vanish over the edge, because magical ice walls) or in a giant mother-ship (complete with dome). If this domed Earth is anything other than a space terrarium style habitat, built by some advanced species, then it must be magical.
How can you even imagine that your entire reality exist within such a pointless cage, what essentially amounts to an insignificant pocket universe at best and a zoo at worst.
So yes, why are you not talking about aliens... the only thing that would make a flat Earth even seem probable... if not fear.
Just to be clear, if the argument you were making was that we lived in a cosmic zoo... that argument would not be so easily dismissed. Then I could understand the reasoning behind a global conspiracy. It also does not defy physics, since any species capable of creating such a habitat, would most certainly be capable of generating artificial gravity. Really, unless you had seen it for yourself (like aliens), there would be no way of disputing that argument with any degree of certainty.
Also, in all fairness, I do not expect anyone who hasn't seen aliens, to be true believers, just as I don't expect them to believe in spirits, or magic, all of which I have witnessed first hand. I realize that I am in fact privileged, not to have to take any of these things on faith... because I have been directly exposed to them repeatedly. Which is why I don't necessarily have a problem with inner Earth aliens... being that I am already aware of stranger things, and am personally convinced that both extra-dimensional and extra-terrestrial beings exist (why not sub-terrestrial as well?).
As far as dragons go... you should be, you should be (a little star wars humor). Personally I don't believe that dragons ever existed, at least not as they are depicted in European culture (probably dinos, stubbornly refusing to go extinct, without a little assistance). But certainly their have been many species of creature to disappear from this world without leaving a trace. More over, Chinese Dragons are another story (since they're extra-dimensional creatures, as are many other strange things... so who knows). The thing is I'm not afraid to acknowledge any possibility... as you can probably tell, i actually gave quite a lot of thought to the possibility of a flat Earth, and under what circumstances such a thing could come to be.