Anyway, here's another link to save me having to unpick this shit (or answer your points directly ); this one arguing a slightly different angle - ie arguing... well, i'm in a rush: you read it (it's more food for thought for me anyway - feel free to give me some contrary links back):
"I call this the ‘biological’ definition of sex because it’s the one biologists use when studying sex – that is, the process by which organisms use their DNA to make offspring. Many philosophers and gender theorists will protest at making the creation of offspring foundational to how we define sex or distinguish different sexes. They’re surely right that sex as a social phenomenon is much richer than that. But the use of DNA to make offspring is a central topic in biology, and understanding and explaining the diversity of reproductive systems is an important scientific task. Gender theorists are understandably worried about how the biology of sex will be applied – or misapplied – to humans. What they might not appreciate is why biologists use this definition when classifying the mind-stretching forms of reproduction observed in limpets, worms, fish, lizards, voles and other organisms – and they might not understand the difficulties that arise if you try to use another definition.
Many people assume that if there are only two sexes, that means everyone must fall into one of them. But the biological definition of sex doesn’t imply that at all. As well as simultaneous hermaphrodites, which are both male and female, sequential hermaphrodites are first one sex and then the other. There are also individual organisms that are neither male nor female. The biological definition of sex is not based on an essential quality that every organism is born with, but on two distinct strategies that organisms use to propagate their genes. They are not born with the ability to use these strategies – they acquire that ability as they grow up, a process which produces endless variation between individuals. The biology of sex tries to classify and explain these many systems for combining DNA to make new organisms. That can be done without assigning every individual to a sex, and we will see that trying to do so quickly leads to asking questions that have no biological meaning."