The motion that gender and sex are separated is not 'new and poorly understood' . It is simple and very well understood, but transactivists have spent about 15 years fudging the issue on purpose, and to this end have exploited the prudish use of 'gender' as a word to replace 'sex'.
What is happening now, though, is that (at least some) transactivists are insisting that gender and sex are different. Since government has conflated the terms in the GRA, they are framing the GRA as being about 'gender' and not about sex, so that changing it is relatively trivial, because 'gender' is simply about personality. Some people who are getting their information from transactivists are wondering what the fuss is about, because having your 'gender' recognised is just like having your sexuality recognised, and not being discriminated against as a minority.
In the responses from organisations to the Scottish consultation on GRA reform, one of the young people from A&B Hangouts, "an online group of trans and gender-questioning young people who live throughout Argyll & Bute" (aged between 15 and 23), said:
'Well, needing medical evidence for gender is equating it with sex. I mean, you can’t really say that your place in society can be sussed out by a doctor. So... I mean, it’s a much more personal thing and I’d say self-declaration would be the only respectful way to go.'
This person clearly has not understood that the GRA is about legal sex. It's not about putting labels on your personality. How many other people have this misconception?