A local TV reporter just interviewed me about the Alito nomination; the questions began with abortion and then church-state issues, but eventually shifted to gender -- aren't women entitled to more representation on the Court than just one seat out of nine?
I responded that gender "representation" is no more mandated than religious "representation." As this post noted, if Alito is confirmed, 22% of the Court's membership will be Protestants (Stevens and Souter) -- if Stevens and Souter would even self-describe as Protestant rather than agnostic -- as opposed to the 52% of the population that is Protestant. Should this be reason to insist on a Protestant instead of a Catholic? Should we complain about Jews' vast overrepresentation on the Court? No; no religious group is entitled to any particular representation on the Court. Likewise, I think, for no gender.
This having been said, I fully acknowledge that Presidents sometimes have considered race, gender, and religion in selecting Justices, as well as other high office-holders. I generally support race-, religion-, and gender-blindness in government hiring, it seems to me the rules may well be different for high-level government officials. (I won't go into the reasons for this here, since they're complicated, time-consuming, and tangential to my main point.)
But Presidents have done this because there are often good political reasons -- both raw politics and politics in a more statesmanlike sense -- for such decisionmaking. They haven't done this because any group is entitled to a certain level of representation; and I think it's a mistake to insist that groups are entitled to a certain level of representation, whether based on gender, religion, race, or ethnicity, in Supreme Court appointments.