I think the idea is not whether we could speculate in a useful way about an FTL or otherwise seemingly impossible phenomenon that we are not yet aware of. It's more about the probability that phenomena and technologies that are far beyond our current understanding can exist or not. In all likelihood we would have the intelligence and technology of ants relative to a million year old civilization. We shouldn't limit what is possible in this universe to what ants are able to comprehend and achieve. Even without such an argument, we only need to look at what we thought was possible 500 or 1000 years ago, and extrapolate forward that in all likelihood our currently understood limitations of physics will all but be irrelevant in 1000 years.
Agreed that it's a flight of fancy to speculate on these yet unknown capabilities, but that doesn't mean they aren't highly likely to exist.
Agreed that it's a flight of fancy to speculate on these yet unknown capabilities, but that doesn't mean they aren't highly likely to exist.