I can understand it, but it's wrong. Because...
You're making stuff up. There never was such data.
This argument has been tried countless times, and it will fail every time. The difference between whites and blacks is not equivalent to the difference between men and women. Absent that equivalency, the argument falls apart.
Analogies, again.
This analogy, that comes up again and again and again, is a great example of why arguments from analogy usually fail to persuade. I look at males and females and see big differences. I look at blacks and whites and see almost no difference except a very superficial characteristics with no great significance. (i.e skin color, hair texture, whatever) So the analogy doesn't focus on what I see as significant.
The people who use the analogy see segregation, and they say, "See! Just the same!"
Which is odd, because they want to maintain segregation.
But, whatever. It's their analogy, so they can use it. It's no more persuasive than any other, though, because the people they are trying to convince are focused on something other than what they think the important similarity is.
If they wanted it to actually work, they would have to say that the difference in sex between males and females is no more significant than the difference in skin color, etc, between blacks and whites, but they don't even try to make that case. Instead, they try to say that the difference in gender between men and women is highly significant, so much so that, unlike the black and white case, segregation must be maintained, but the difference between the sexes is not very significant that it must be discarded.