"So what's the answer? There isn't one, at least if we're looking for the answer in biology. We must not fall back on biology."

Rather, the vast majority of people - both in academy and in the laity - recognize that sex is primarily and enormously genetic. It's regretful that so many people don't understand the genetics, but this is no excuse to force comprehension to an emotional, rather than rational, standard. 

"Rather, we must always remember that it is we, not biology, who decide who counts as male or female."

This is demonstrably false. Biology is responsible for the majority of this 'decision', as the author rather poorly puts it. I think the author means to say that where individuals seek to deviate from this standard, we are obliged to accept their choice. The author needs to be considerably more careful in his demands for a reasonable ethical standard that he does not put his foot over the line of his comprehension. Or more briefly: leave sex to the experts, please.