AWS are controversial to begin with, but they can be justified on the basis of specific structural barriers and prejudice faced by women, and on the basis that women are 50% of the population, therefore equal representation is a reasonable aim.
If women could simply identify out of being female, there wouldn't be any need for AWS.
Labour are of course free to push the fringe view that 'woman' is just a catch all term for 'minority group facing oppression', but they will relegate themselves to being a fringe party.