No they are not sharing wrong, the system is broken.
Google+ offers many ways for me to target content to a group of people that I personally know, and only one, "Public", to distribute content to anyone who might be interested.
Unfortunately there are at least 3 common use cases that need to be considered:
1. I target a message to people I think are interested. (Google+ does this well.)
2. I broadcast a message to people who may be interested. (Google+ sucks at this.)
3. A group of people forms for some purpose (work, game, whatever), and needs to be able to communicate within that group. (Google+ has no support at all for this, and the result is that I was forced to go to Facebook to communicate with people I was playing a Google+ game with.)
There is a real need for all three modes, and I don't know of anyone who does all three well.