If you have yet to run across posts on elevatorgate/rebeccapocalypse (over 9,000 Google hits on the former term) then you probably don’t read many science/skeptic blogs. If you have and are sick of it, don’t worry, because I’m not going to add my quanta of coinage. I have come to loathe participating in internet discussions of this ilk — despite the community supposedly being held among the science/skeptic minded, they have a tendency to stray from rationality and civility far too quickly and too much in magnitude for my taste. In many cases, if you don’t present the right answer™ as determined by the owner of the dais, you are quickly dogpiled into oblivion, and that can extend to any kind of criticism. Point out someone has misquoted Evil Protagonist (or note that EP was actually correct in some statement) and all of the sudden you are a staunch supporter of Evil Protagonist in the eyes of some (many?) participants.
However, in case you want more of the same or are otherwise interested in a somewhat related topic, here is a post by xkcd’s Randall Monroe on Google+’s insistence on publicly disclosing your gender, which does not seem to have descended into the usual quagmire, though it does include the predictable “it doesn’t bother me so it shouldn’t bother anybody” responses.
The bottom line is that there are a lot of reasons Google+ would want to ask about your gender. But there’s no good reason to pointedly make it the only thing in your profile that can’t be private—and many reasons not to, starting with basic courtesy. It may be a small issue in the grand scheme of things, but I think it’s worth getting right.