In other words, the court agreed with Cormier’s perspective that transgender women are not women and that she never should have been expected to understand that a locker room for women would include transgender women. By not disclosing that it was taking the opposite position — respecting transgender people according to their gender identity — Planet Fitness was “failing to reveal a material fact” in an attempt to “mislead or deceive the consumer,” as the relevant Michigan law reads.
This is the crux of it for businesses. If they are going to have policies that make intimate spaces mixed sex then they need to be very clear to their customers this is the case.
I agree that this is an action that everyone can take right now. Write to your gym and ask if they use the permitted exemptions in the Equality Act to retain sex-segregated spaces. If they don't, they ought to be making it explicitly clear to all their customers that they could encounter a person of the opposite sex in their changing room. Just like signs are put on the doors of toilets to let females know a male attendant is currently cleaning in there.
I support all businesses having male, female and unisex facilities. Not only does it offer a solution for transgender people, it offers a space for fathers to accompany daughters, and mothers to accompany sons, or somewhere to use with an opposite sex carer or an extra toilet to use when the ladies has the inevitable queue and someone is too desperate to wait.