DB's main argument seemed to me to be that this change in the law wouldn't affect the law, only the operation of the law.
She then spent quite a bit of time arguing that it wouldn't even affect the operation of the law - it would be operating in the same way for more people. But not many more people. Hardly any, really. And anyway the UK government had thought about adding even more than that (ignore the fact they'd decided against it) so the tiny Scottish numbers didn't count. Besides which the argument said 'might', and that's not evidence in the way that saying 'would' is. And some of the arguments might be wrong even if others were right - and if some of them are wrong that casts doubt on the ones that are right. And you don't need a birth certificate anyway, so it's all fine.
I think that was it.
Although I must admit I got bit lost around the point about it not being a problem if people couldn't use an employee of the opposite sex being paid more to prove pay discrimination, because they could use one of the same sex being paid more instead.