I'm not sure if legitimizing is the right word. If the human brain is the source of all of our gods and related beings and worlds, that wouldn't necessarily make them real.
Then the brain, a very physical thing with all its chemical reactions, cannot be the ultimate determiner of which metaphysical phenomena is real or not.
The question would be, are there any that are real? How would we confirm that, if we have defined them in such a way to make it impossible to do so?
Good questions, if the brain can't, who or what makes the ultimate decision on wether something like desire, longing, melancholy is actually real?