Flat-earthers, geocentrists, cargo cultists, and phrenologists have been falsified by the facts. Relativism removes any reason, besides sheer whimsy, for changing one's beliefs. If my belief makes something true, there is no objective warrant to alter my beliefs in the face of argument or evidence. Such an attitude applied to medicine or science would be deemed ridiculous. Medical doctors have good reason not to bleed their patients, as was commonly done for centuries.
Biologists have good reason no longer to believe in the spontaneous generation of insects from mud.
Human subjectivity untethered from objective constraints is a shallow and shabby thing. When it reaches a certain stage we call it stupidity or even insanity. Remember Heaven's Gate. But this is the very thing it cannot be. If truth is only a function of individual preferences, one cannot escape the prison of subjectivity in order to make objective statements that supposedly apply to all of reality.