Updated by MNHQ with a tweaked version of the OP provided by @Mermoose. That's why the thread appears to go a bit peculiar halfway down.
It's argued that existence of people with DSDs (or intersex people) means that the female category now contains males, and vice versa.
There are two problems with this that I can see, the first being that DSDs don't literally make people 'intersex', they're conditions that affect male people and female people.
The second problem is that even if it were true that some people were neither male nor female but somewhere in between, that wouldn't support the idea that male people now belonged in the female category.
If we did this with sex, why not do it with other categories? I've decided to put together a list of other categories that, due to fuzziness at the edges, should now contain their erstwhile opposites. Feel free to add affected categories.
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Green exists, therefore blue is also yellow
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The exact moment of death is very hard to define - it used to be that when the heart stopped, you were dead, but now it's usually when your brain stops working. Dead people are now alive and vice versa
*Species. I mean, we just can't keep species as meaningful categories if we're getting rid of sex. This is Richard Dawkins:
"so-called ‘ring species’. The best-known case is herring gull versus lesser black-backed gull. In Britain these are clearly distinct species, quite different in colour. Anybody can tell them apart. But if you follow the population of herring gulls westward round the North Pole to North America, then via Alaska across Siberia and back to Europe again, you will notice a curious fact. The ‘herring gulls’ gradually become less and less like herring gulls and more and more like lesser black-backed gulls until it turns out that our European lesser black-backed gulls actually are the other end of a ring that started out as herring gulls. At every stage around the ring, the birds are sufficiently similar to their neighbours to interbreed with them. Until, that is, the ends of the continuum are reached, in Europe. At this point the herring gull and the lesser black-backed gull never interbreed, although they are linked by a continuous series of interbreeding colleagues all the way round the world."