On the narrow point at issue, I agree with Yglesias and Greenwald that the conflation of sexual identity with someone’s “sex life” is silly. I’m reminded of my favorite example of this, opponents of gay and lesbian rights attacking John Kerry for mentioning things about Mary Cheney that were allegedly supposed to remain between her, her partner, the Coors Corporation, and gays and lesbians that Coors wanted to sell beer-colored horse piss to.
Having said that, I’m not sure I fully endorse Greenwald’s argument here. The last bit of snark about Cheney indicates a major difference also present in Greenwald’s analogy about Kevin Drum: I think there’s an important distinction between what people voluntarily reveal about themselves and what they don’t, a distinction that’s especially crucial if they’re leaving other people alone. It’s worth noting, first of all, that speculation about Kagan’s sexuality is driven entirely by quite pernicious stereotypes — assumptions about her haircut, the implicit assumption that no adult could simply choose to be celibate, etc. — as opposed to any actual evidence or anything she’s said about herself. (Greenwald’s point about some Good Liberals assuming that Kagan is a lesbian is unserious — surely Greenwald has met plenty of professional Good Liberals prone to heteronormative assumptions.) This is a complex question, but I think there are real potential violations of the dignity of individuals inherent in trying to force them to define their sexuality into a convenient box when they’ve chosen no inclination to do so themselves.
Many of you will remember similar questions being raised about David Souter, because of his lack of conformity to certain norms about the lives adults of a certain social status are expected to lead. Would the polity have gained anything by asking Souter to publicly define his sexuality? Not that I can see.