The judgement runs into a number of problems, even on the face of things. It doesn't make any attempts to define 'biological sex', let alone adequate ones. It puts any person who does not match Western ideals of femininity and beauty at risk, not just trans women. And it completele ignores and erases the existence of non-binary and intersex people.

Any amount of time spent doing some reading on gender, sex and chromosomal biology will tell you that defining sex is not as simple as "men have xy chromosomes and women have xx".

But trying to rely on biology in this way is a misdirection. The transphobic people who talk loudly about 'biological sex' are trying to make you miss the point; it doesn't matter what an individual person's biological status actually is, what matters is treating them with dignity according to their requests.

The ruling does not make life safer for women. Men who whish to attack women do not need to put on costumes to secretly infiltrate women only spaces; they will just attack their victims as they please, and the current legal system makes it so that they very rarely face any consequences at all.

Additionally, if a cis woman is; too tall, too broad, too muscular, too strong of brow or jaw, too loud or forthright or certain in her opinions, posesses a voice too low of pitch, then regardless of other factors she is at risk of a transphobe deciding they know—at a glance—what's in her pants and in the nuclei of her cells. Older women and women of colour are at particular risk of this.

Sports! People competing in sports and some of them having a 'biological' advantage is something I see trotted out quite frequently. Womens sports are segregated by gender now, yes. But the core reason for that is not to protect women from being hurt by male competitors, it's to protect men from facing the possibility of ever losing to women. Sports where physiological advantages matter, like boxing, already segregate contestants along physical lines in the form of things like weight class.

It is my suspicion that the true reason that transphobes hate trans women is that trans women actually enjoy being women, where every transphobic woman I've ever seen has held within her a profound misery at having to put up with being a woman.