How does one criticize the rampant abortion of girls while still defending abortion in general as a perfectly valid choice? There is no simple answer, but it is vital to recognize that abortion itself is not the problem.
Stevens is right. There is no simple answer for pro-choicers because there is no valid answer. If you accept the ideology that women should have complete bodily autonomy and you live by the slogan "Trust Women" then there's no weaseling in a "well....I'm in favor of bodily autonomy for women whose decisions aren't effected by cultural differences" or a "Trust Women.... whose choices I agree with."
It reveals that some pro-choicers actually only "trust women" to make choices they agree with. "The Trust" is there if you want to abort because you're poor or young or just don't feel ready to care for a child. But the trustyness factor gets a little foggy when you want to abort because you desire a male child over a female one.