What the case highlights is sadly there are criminals who will follow girls into toilets and commit sexual offences - rare but it happens. And whatever the legal status of the perpetrator the offence would have happened.
Firstly, the social and psychological framework that prevents males from entering female toilets is actually a protective factor currently. Because those who do not look like they belong in the female toilets can be kicked out, or security can be called. Self-ID would erode that layer of safeguarding, in my view, because I guarantee you that if someone can say they are "legally female" the fear of litigation would be an extra layer that prevents people from challenging the presence of male-bodied individuals in female-only spaces. The social ability to ask "hey, do you belong here?" is actually useful to protecting individuals within that space, in my opinion.
Secondly, there is a real difference between someone who is able to regularly access female spaces or someone who enters them once or twice "covertly" in a predatory manner. In this example, the perpetrator accessed female toilets at least twice, which makes me wonder whether they had been able to do so for a long time and gone unchallenged, which makes me wonder if there were other incidents that weren't reported. In crime there can be a tendency to "build up" to an offense - an escalating pushing of the boundaries until the offender commits their most serious assault. This is why the legal status of the offender is actually a relevant factor to consider, in my view.
Thirdly, if there is even a theoretical possible additional risk to females being preyed on by those who abuse our current systems then this needs to be looked at properly and discussed - not hidden away from view in strangely-worded articles. I would like some accurate statistics so that we could have a real understanding of whether the risks are hypothetical or real, and be able to really track changes.
Finally, saying "this would happen anyway" when it comes to a sex offender targeting two girls, aged 10 and 12, on two separate occasions in public single-sex toilets where they should be safe, is just not good enough. This is about safeguarding the most vulnerable. I find your attitude cavalier. If there is a potential loophole in our laws that makes it easier for offenders to normalize their presence in single-sex spaces in order to target such innocent victims, then I want to identify it and fix it.
What worries me even more is imagining (completely hypothetically) that the predator was in the toilets for a while, acting suspiciously, and other (adult) females noticed them but didn't say anything because they didn't want to challenge that person's presence there or be called transphobic. But if they had been able to speak up, perhaps these girls would have been safe in such a theoretical scenario.