Deep down, in the core of your soul, do you feel like you are living your life in a singular reality? Regardless of the possibility of multiverses, we have all managed to co-exist in the same reality for as long as we can possibly remember... There was never any time when you said, "hey dude remember the time Josh disappeared into the multiverse for a while and came back? That was weird."
We are following a most linear path through time which is guided by inflexible, unchanging rules, laws, formulas, etc., and even if we do not know exactly what the formulas are that govern what is happening in our reality at any particular moment, we accept that an absolute truth behind these laws and formulas does indeed exist... for if we did not, we would have no basic principles of knowledge on which to build upon and we wouldn't be able to figure out anything technically advanced at all.
Ergo, at any given time in this universe, there is only 1 reality, only 1 way in which a particular set of events can unfold due to the steadfast and dilligent application of the unbending rules of physics, chemistry, mathematics and astronomy. We can have different interpretations of the same event but when one begins to abandon science, logic and reason in the face of emotion, ego or stoicism, they are indeed abandoning the one reality and not in fact creating a new, equally valid second reality. These realities do not now coexist because only 1 of the realities ever existed in the first place.
So indeed the world is now full of "ghost realities" which only serve to confuse and madden those who happen to cross the paths of their vessels. On the other side, those who have respect for science, logic and education, and are willing to admit when they are wrong and correct themselves in order to perpetuate ideas more closely in alignment with reality are doing a service for humanity by helping to spread true understanding. It is indeed true understanding because it can be used to successfully better oneself by applying it to our 1 reality, of which, of course, there is only 1.