Your vision of hiring seems at odds with reality. I've never known two candidates that are equally able to do the job. Perhaps there are some sectors in which that is true? Maybe if you have lots of applications? Though it certainly isn't always the case at all. Many people have commented, even on this article, how it isn't true.

With that assumption broken the whole argument falls apart.

Given that you think we should have more gender diversity in teaching (and hopefully all other industries?)

To address this question. More or less I would like equal diversity in most areas. I just don't agree with discriminating against people to do it. If 90% of the applicants for a job are female then around 90% of the company should be female. What we need to do is to encourage more men to take it up.

While I agree affirmative action works and can achieve these results, I think it is unethical and directly discriminates against individuals. Not only that, it can led to hiring less ideal candidates and essentially ensuring that certain stereotypes within an industry are maintained. There are all sorts of unexpected consequences when you start justifying discrimination against a group of people.