Yoshino's response is valiant and mostly well argued by scholarly standards, but I can't help but wonder why he chooses to dance around the slam-dunk refutation of George:
... it might surprise many couples who cannot have children (or choose not to do so) that the validity of their marriage rests on its "orientation" toward procreation.
Why the parenthetical? Why not go straight for the jugular? It is precisely the heterosexual couples who choose not to have children that are the inarguable refutation of George's position. No need to quibble over whether homosexual orientation is a choice or not: people who undergo surgical sterilization are indisputably choosing a "lifestyle" that is incompatible with reproduction. Not only that, but there can be no dispute that they are making this choice deliberately and with the express purpose of thwarting reproduction, as opposed to homosexuals, for whom the obstacles to reproduction are arguably in some cases merely a side-effect of the actual objective.
There is no possible way to argue for the invalidity of gay marriage on the grounds that marriage is inextricably bound to reproduction without taking the position that people who have voluntarily sterilized themselves are not entitled to marry. That's it, the whole megillah, period, end of story. The fact that not a single sane person would be willing to take that position reveals George's argument as just another instance of thinly disguised bigotry against gays.
What is harder to understand is why left-leaning scholars like Yoshino relegate this argument to parentheticals instead of putting it front-and-center where it belongs. Instead, Yoshino takes his eye off the ball and allows himself to get drawn into a quagmire of quibbling over sports analogies. I really don't get it.