If we accept the philosophy of reality only existing in the perception of the human mind, then what is to distinguish your "alternate reality" from the universally accepted "general reality"? A table, for instance, is said to "exist" because (and only because) it is perceived through our senses by our mind, for we can in no other way prove its existence objectively. These "alternate realities" of yours exist only in your mind - however, that kind of existence still does not differ from our general guidelines of explaining our world, with the key exception that the generally accepted "reality" is perceptively experienced by the majority.
Philosophically, however, you could argue for the acceptance of any reality 'perceived' by the brain, for ALL reality 'exists' as a result.
Questions of science, science and progress, do not speak as loud as my heart...