"just that the nursery feel they have to explain a decision to dress girls one way and boys another in case parents object. "
I would want an explanation, if my GD Nursery did this.
I put up with that shit 45 years ago (when I was in Primary) and with my DDs.
There is no reason to make choices or divisions based on the Sex of the child.
OP go onto the thread about "you should have asked", which is about the constant mental load Women carry, even if the physical housework is shared.
We should all be working to remove end this, as we did with all the other "isms".
However, I can remember the backlash when people stopped 'blacking up' and children were no longer 'blacked up' for plays, or races stereotyped.
If MN had have been around in the 70's, we'd have threads like yours asking what the issue was.