This is the craven "free-market" excuse. Its hardly that simple.
First of all, the woman who opposed having to see the naked man in the woman's shower was attacked as a bigot. Secondly, what spa will ever be safe for her and people who think like her, if men-pretending-to-be-women are allowed anywhere?
What would happen to a spa that says - we definitely do not allow mis-gendered or transgendered people - come to our spa!? I'm sure you have heard of the baker in Colorado who refused to bake a cake for a gay wedding. They man has been persecuted by the state and the gay mafia for the last 10 years.
Then should turn their anger against those of their fellow women who have been yapping for years “trans women are women”. Shun any woman who says that. Scream in her face that she’s a lunatic.
Nothing will change until that happens.