Why quote just one, when all are the posts of a person with a sexist attitude? Take your pick.
As to why they are sexist, consider Group A, who has benefited from the oppression of Group B for generations. Any member of Group A who thinks any gain in equality by members of Group B is a harm to members of Group A is not supporting real equality between members of Groups A and B. When members of Group B begin to acquire some of the benefits of being seen as equal to members of Group A, members of Group A will by necessity be giving up some of the advantages they have enjoyed exclusively. In the case of women gaining opportunities that have been denied them in the past, men who see this as harming them by taking away their own opportunities are sexist.
There are only finite numbers of opportunities available in society. Giving some of these opportunities, that used to be exclusive to men only, to women, means some men are going to lose these opportunities. There's no way to get around this, and to object to it because it takes something away from some men is sexist.
So if you are the kind of man who thinks "well ok, I don't mind equality between the sexes as long as I still get everything I want, and so does every other man", you're a sexist, because you see any advantage achieved by women as taking something away from you. Something you as men are entitled to simply because you are men, and shouldn't have to sacrifice to anyone else unless it doesn't cost you anything.
The issue raised in the original post was the myth that boys are experiencing a crisis because girls are outperforming them in school. To see this as a crisis is sexist, to argue that it is a crisis is sexist, therefore you can choose any post you please that argues for the existence of a boy crisis being caused by girls doing better in school. It will be sexist.
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