What about the idea that parallel lines do not intersect and that there is exactly one line through a point parallel to another given line? These were thousands of years old and well accepted until pretty recently.
Actually, that axiom made even the ancients uncomfortable. There were lots of attempts over the centuries to "prove" or "disprove" it.
The fact that violating it can still produce a self-consistent geometry was what was stunning.
But this would still be an extremely useful effect if it does exist, for devices designed to focus it. Look at how an electric field's influence on semiconductors has almost no relevance to anything except when harnessed just right.