The current American mainstream view limits gender to just two flavors. MALE and FEMALE.  The widespread acceptance of this model offers no place for any identity other than MALE or FEMALE, and the two are viewed as mutually exclusive.

While many trans people do claim "male" or "female" with alacrity, the fact remains that they are not the same as bio-males or bio-females.

A transgender individual socialization and childhood experiences, and the lengths to which they must go to live as self-actualized adults, are beyond the wildest imaginings of their bio-male and bio-female friends, partners, and relatives.

I find it difficult to accept this model.  My hope is that someday there will be no binary view of gender.  That gender will be recognized as an aspect of a person's core identity rather than a social construct. 

The gender continuum would then become a non-linear spectrum with each individual finding their place on this spectrum.