While one often hears “But they aren’t even 1% of those competing in women’s sports” as if the ethical issue is one of numbers. “It’s fair as long as there are no more than x% of them” is wrongheaded on its face. Wrong is wrong. Unfair is unfair.
That’s true. I heard a feminist on the radio saying that trans people make up only a small proportion of the population, so, who cares? Yet, each individual is a whole world. I’ve heard trans activists saying there were “only 2 or 3 rapes” in a women’s prison by a man dressed as a woman. Again, not a good argument.