Well why not let 20 year olds compete against elementary school kids? Or 200 pound boxers or wrestlers compete against 100 poumd athletes. Or stop having special olympics for the mentally handicapped, or wheelchair olympics.
The divisions that are there now exist to create fairness. We are doing a pretty good job. There will always be exceptions, but rules should not be made for the exception. There are binary people too. I am not advocating an absolute rule but it is also not fair to let anyone just show up and say he is now a woman and compete.
Throwing away all the rules to benefit less than one percent of the population is not fair. It is oppressive to women. The divisions that are there create fairness. Trans people seem to want fairness only for themselves and it is very sexist.
I am not as concerned about the highest levels as i am about the lower levels. Your basic high school in anytown usa. I have been involved with youth sports for a very long time and am very familiar with the difference even one year can make, or the differences in boys and girls.
If you did not have divisions at the younger ages there would basically be no women advancing because they would never get the chance to develop at the early stages. By the age of 15 it is pretty clear if an individual has what it takes to be an elite athlete. Even earlier. If there was not a sex division no girls would get that elite standing and would not develop into all they could be.
Women have had a long struggle to achieve what they have. Women's sports are being taken seriously now. I just can't see why people want to oppress women and destroy the progress that has been made.