Many women grow up with a sense of physical vulnerability that's hard for men to appreciate. Our culture's relentless treatment of women as objects teaches them that they are defined by the one thing that men around them want from them—men who are usually bigger, stronger, and (like any human) occasionally crazy. This feeling—often confirmed by actual experiences of harassment and assault—can lead, understandably, to a lifetime of low-level wariness and sense of vulnerability that men have trouble appreciating. A male designer building an interface should try to keep in mind that there are reasons a female user might feel uncomfortable being told she has to broadcast her gender. Sure, someone's gender is usually obvious from their name, but there's no need to force people to draw extra attention to it—introducing myself with "Hi, I'm Randall." sends a different message from "Hi, I'm Randall, and I'm a MAN."
It's not something that most men will feel particularly sensitive to, but perhaps they should. Most people would be concerned about a website that asked users to publicly display their ethnicity or skin colour - and the situation here is not all that different.
Seems like Google+ has had its share of unintended consequences of apparently minor design decisions. Let's hope they listen to this feedback and act on it.
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