AGAA4 Eddie Izzard isn't going to change the world, much as he sees himself as a trailblazer; but the idea that 'gender' is the same as sex may well do just that - it would have done had Stonewall had its way.
In a world where sex (as opposed to 'gender') is optional, women have nowhere to call our own, no sex-adjusted categories in sport, no right to meet without male supervision, and no words to describe us as women and girls, so we can't even talk about female concerns as there is no vocabulary to do so.
Any research into sex-based societal differences, from pensions to employment to health are meaningless when figures for male and female participants can't be compared with any accuracy, so targeted initiatives stop.
Crime figures are similarly skewed - even definitions of crimes such as rape are impacted. Rape has always meant 'non-consensual penetration with a penis' (ie male sexual domination that could lead to pregnancy, STDs, etc) but we are now told that women (or more accurately 'men who say they are women') can commit rape, so there is a call for the definition to include penetration with an object. I won't stop to a discussion of which is worse, as that is absolutely not the point. The point is that when we even think about removing a massively significant crime from the 'books' in order to mollify those who don't see women's rights as remotely relevant, we should be asking ourselves why.
Personal dignity (eg dealing with periods) and safety when vulnerable, eg in changing rooms, hospital wards and public toilets, where women and girls might be ill or in a state of undress is lost when men can access all areas.
Women's categories in the Arts are pointless when (for example) a man can win the Women's Prize for Poetry or whatever, so a female perspective on life goes back to where it used to be in the days when women used male names to be taken seriously. It goes on and on and on.
This is not about discrimination, and it is not a triviality - it is much more serious, and however much we are told it is about 'being kind' we really need to protect our daughters and granddaughters from the insidious sidelining of women and girls. The tide has turned a bit, but we can't rest on our laurels.