Obviously it would have been very hard for people in society to put aside their prejudices and ignorance and co-exist but that doesn't make it impossible.
Fantasy isn't impossible, just so very nearly so as to make it nonsensical for us pragmatic types.
Industrial Age people, living (long term) side by side with Stone Age nomads isn't going to happen now, or a billion years from now; nor was it going to happen then. It has nothing to do with predjudice, nor with ignorance.
One group (BTW it will always be the one with better weapons and tactics) will assimilate or annihilate the other. The occasional battle may be won, but the outcome of the "war" is chisled in the granite of reality.
Stone Age folk still exist today in tiny little groups in a few of the more dense rain forests, but their days are numbered. By the time the Human population begins to approach 10+ billion, the areas that they depend upon will (as they know them) be gone. Game over.
Maybe someday, if humans evolve into "ethereal" beings of some sort, wholly different societies could share the ether together without any conflict.
Methinks that until then, us corporeal humans will continue to scrap over patches of ground to tame and conquer.
Will feelings get hurt? Yep. Will whole peoples be oppressed if not obliterated? You betcha. But at the end of the day, the manifestos of those three revered philosophers Woulda, Coulda, and Shoulda, won't mean squat. History will just roll on by without them.
Just ask an Inuit hunting seals with his .223 and his "snow go" if you don't believe me.