Stacey May Fowles explains why she has made her Twitter account private: because she is afraid of men on the Internet.
There's good reason for this fear, and it's likely one you'll empathize with if you're a woman who has ever dared to have an opinion in the techno-public realm. In fact, women have never once asked me why my account is locked—and unlike some of my male editors, they've never recommended opening it up. They understand that the online world has become a horror show, and that men largely drive that horror. Men are usually the ones who post nude pictures of their exes, release the home addresses of the women they dislike, and run the vileness that is Gamergate. (I'm even reluctant to type the word Gamergate, as if doing so conjures the hoards like some kind of Internet Candyman.) Of course, Not All Men, but unless a new Twitter follower has "I hate women" or some variation thereof in his bio, there's no good way to predict which one will decide to take offence at you merely existing. And there's no way to know whether that person who is offended will be the one to threaten to end your life.
Expressing this fear (especially the decision to limit others' access to oneself with technical mediators such as block lists) invariably results in dudes becoming angrier, demanding participation, and narrating—to as broad an audience as possible—one's contemptible efforts to avoid open and honest dialogue.
This behavior is often couched as a vigorous defense of free speech. But it's about extending the public space as far into someone's personal sphere as possible, to punish them for trying to participate in it.