It's odd that the article juxtaposes the ‘Let Girls Be Girls’ and ‘Let Toys Be Toys’ with the nasty feminists who have a very narrow view of what it is to be a woman, as if it is two different things. As if, used correctly Mumsnet is a good thing but used badly it is a hot bed of transphobia.
But all the above is just different facets of the same argument, which is that gender stereotypes are limiting and harmful to boys and girls and have little to do with the realities of the sexed body.