He's wrong for a more fundamental reason. He asserts that the Boy Scouts unjustly discriminate against him and other men for what they are, when in fact it is a behavior choice that is unwelcome.
These same men assert they are unjustly denied the right to marry when in fact they are only held to the same standard as other men: they may only marry women.
The moment you accept as true the false claim there are more than two sexes in the human race, you have already lost the central battle in this culture war. Arguing over taxes dollars, and donations are meaningless skirmishes by comparison.
My criminal law class is having a raging debate over this very point right now, with a case involving alcoholics being arrested for being intoxicated in public. (Are they being arrested for being addicts? For doing some wrong act that they cannot prevent themselves from doing? Or are they simply being arrested for committing an illegal act that they have control over?)
The distinction is a very fine one, and easy to get muddled. It also has wide-ranging implications in law.