The author is saying that we need to balance the cost to men using mens spaces with the cost to women if they use women's spaces.
We do this already. We recognise that very small boys cannot use mens spaces alone, therefore their mother may take them into the female toilet or changing room.
Legislators assessed the risk of male people in male spaces and concluded that 4 year old boys sometimes needed the protection of the women's spaces.
Not short men, old men, gay men, disabled men, not men on medication, not men who've had surgery.
Its been thought out already, and the conclusion is small boys sometimes need to use the space, not men.