Choice is generally good in my opinion. Considering what the majority of Github is as a community I would very much doubt that the majority is going to be making their profiles private. Making it private makes no sense if you collaborate and contribute with open source projects (or host your own), and it doesn't help with having a public profile that you can potentially show off to companies you want to be hired by.

So who is this feature for? Those who have no interest in the social aspects of Github and want to use it privately. I'm sure that's going to be a minority.