Sexual Orientation, Sex Life, and Elena Kagan

Glenn Greenwald wrote the following today:

Perhaps it's naïveté, but I've been amazed by the outraged objections of many Good Liberals to the mere discussion of Elena Kagan's sexual orientation. Without realizing it, they've completely internalized one of the most pernicious myths long used to demand that gay people remain in the closet: namely, that to reveal one's sexual orientation is to divulge one's "sex life."

Well, he's got it part right, and part wrong. He explains:

The Appropriateness of Adjectival Nouns

Ok, so this is probably a slightly different subject from what many of my other posts will be, but I'm a huge linguistics nerd too, so I thought I'd kick it off with this, based on a discussion a few of us had a couple weeks ago.

So here's the main question: Is calling someone an "[adjective]" as a noun versus an "[adjective] person," inherently offensive labeling, or is this usage somewhat an accident of language? For example, we can all pretty much agree that calling someone a "schizophrenic" versus "a schizophrenic person" or "person with schizophrenia," is offensive, but is it always the case?