Someone said to me earlier "but didn't they decide years ago that trans women could compete?", and I had to articulate (to myself as well as this person) what the real difference now is and why it matters.
In 2004, the IOC decided that transgender athletes must fulfill three conditions - they must have had reassignment surgery, they must have legal recognition of their gender, and they must have had at least two years of hormone therapy.
This new decision removes the requirement to have had surgery, and that is why it is worrying. The statistics tell us that approximately 80 - 85% of trans people do not have reassignment surgery - before I read up on this, I blithely assumed that surgery was the norm, but it isn't at all. So many more thousands of trans women who were not previously eligible to compete, now are. And, as inevitably happens in trans issues, the benefits to the trans population are celebrated, while the potential harms to women go unacknowledged.
Incidentally, where are the intact-penised transwomen athletes showering after the events, I wonder? And when squads go on training camps together, do the natal women in the team get a choice about whether they share a room with a pre-operative transwoman or not? Would they dare to object? Or would they just get dropped from the team for being bigots. I wonder.