No political party today would argue that they ought to be allowed to discriminate against women.
We know they do, because we can look at the results:
That high point in the Labour graph was from 1997, when half of all constituencies with winnable seats were required to have women-only shortlists.
Of course men complained about this, and men’s reasons for complaining are obvious: this system meant that party activists who had earned and deserved a chance of winning a seat, would, in 50% of constituencies likely to go Labour, not stand a chance of being selected. That is to say, in just 50% of constituencies between 1997 and 2003 (when legal challenges from disgruntled men forced Labour to drop the policy) the men were in exactly the same position as women – and they didn’t like it.