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During the early years of the women's movement, sexist language was a hotly debated topic. Many people, both men and women, felt there was nothing wrong with using he to mean he or she or with using words like mankind—and they resented being asked to change their ways. They argued that according to tradition everyone knew that such terms included women.
Feminists attempted to expose the absurdity of this view with sentences like these:
Man, like the other mammals, breast-feeds his young.
Everyone should be able to decide for himself whether to have an abortion.
In addition, feminists argued that sexist language has a powerful negative impact on women: It makes women invisible, reinforces stereotypical gender roles, and limits women's opportunities and even their aspirations.
Today those early battles are largely over. Many people, both men and women, now find sexist language offensive. And most writers, no matter what their personal feelings on the issue, don't want to risk offending readers.
Any remaining controversy centers on ways of avoiding one form of sexist language: use of the generic he. See Pronoun-antecedent agreement.
Source: Hacker Handbooks (Boston: Bedford, 2013).