TW claims that they know women don’t object to them being in women only provision because they aren’t confronted or challenged overlook social/cultural norms. This simply isn’t an accurate measure.
TW who decide that they pass and base this on self assessment or what friends and family tell them are not using appropriate sources.
TW who say that there is no point in a law that is dependent on self policing need to look around themselves. Most of the laws that impact me on a daily basis depend on individuals voluntarily adhering to them (traffic regulations, environmental laws etc). These laws are supported by enforcement mechanisms like penalties for violations, but rely heavily on personal responsibility and societal norms for compliance.
The gotcha about gender non conforming and butch women being challenged is an unfortunate byproduct of what has gone before, at the hands of trans activists. Being asked if you are female, when due to being perceived as masculine, is easily resolved through speaking. At worst, this is uncomfortable for a female being challenged this way, but nothing worse than that. Signs and campaigns can ask females not to challenge individuals and instead provide an alternative mechanism for raising concerns/objections. TRAs won’t like this as they don’t want any objections to be legitimised.
If they continue to defy the law, it is likely that campaigns to instigate enforcement penalties in the form of fines and convictions. These won’t be hard to police as evidence will need to be produced to evidence natal sex. A swab test will suffice, which is no more intrusive than a breathalyser and is proportionate as determining sex is essential information to the investigation.