What Is Ableism? Can We Truly Be Able?

As I read Margaret Price's Introduction to Mad at School: Rhetorics of Mental Disability and Academic Life.

With regards to the norm, Price writes that the disclosure of mental illness (as well as queerness) is "apparitional" and that it is only disclosed when the environment in which it is present allows it to disappear and appear. I think that this is a point of discussion because as we have sort of discussed in class, this 'norm' is something that is not particularly well-defined and changes depending on the individual. If we cannot define the 'norm', then can we really define the 'other' or the 'deviant' as a society as a whole? How can these deviations "appear"?

But, as with physical disabilities, it is difficult to push past the binary of the well/unwell paradigm in terms of mental illness. However, if the "deviations" are not fixed (and as Price has pointed out,  these so-called deviations can be anything from "coffee-guzzling, cigarette-puffing, vigorous human beings" to people who have been diagnosed with mental illnesses through the DSM) and neither is the "normal", then what is "ableism"? It is difficult to define this term if what its definition is based in is so rooted in other factors which themselves have no clear definition. 

This 'category' of being 'normal' and 'able' seems to me to be nonexistent. If this is the case, then why are we so good at finding disability and deviations? Why are we so good at 'othering' those that do not fit in this non-existent norm when we, ourselves, probably do not fit in either?