Katie K is one case. There are others. How many is acceptable ? You’ve already been asked this question by another poster.
Primark recently announced they would be returning to single sex changing rooms. A few months ago an off duty police officer was caught filming a mother and daughter in a mixed changing room. He was holding his phone under the partition. There have been other instances but this lead to their change of policy.
There’s also a thread on here where women were asked to post examples of incidents that had happened in mixed sex spaces, such as gyms, swimming pools, changing rooms. It’s sickening, and goes on page after page.
Yes, a predatory man could hide in a female toilet. But he would have knowingly gone there uninvited, and women would know he shouldn’t be there. The #bekind movement wants to invite men in purely on the basis that they say they are women. So that’s the green light for your predator.
Lots of people don’t like mixed sex changing rooms, but often now there’s no alternative. It’s also socially awkward to say so, and some organisations will take exception. It’s usually resolved by self exclusion, people just feel too uncomfortable to use the facilities. So they’re actually the ones being discriminated against.