The difference is that the connections on G+ hold much less meaning than the connections on Facebook. Facebook automatically populates specifically-named friend lists based on your network data and asks that you refine their lists to improve their data collection.
Essentially, users who choose not to provide Facebook with their close friends, family, university, and location will be scoped out and tagged by their own friends using these smart lists. It's a disturbing strategy for data collection.
I have a problem with the way Facebook allows me to share links. Even by using your 'advanced' login security measures, I have been required to fill in CAPTCHAs hundreds of times for legitimate links. For instance, why is a link to an imgur JPEG file considered possible spam? Do you not whitelist domains? And isn't the repeated use of CAPTCHAs generally an abuse of the actual purpose of a CAPTCHA?
Additionally, Facebook has disallowed me from posting specific legitimate links. You've failed as a communication medium when you censor links. There was no indication that anything was wrong with these links that I shared with friends. There's no excuse for this practice.
Yet, at the same time, you allow seriously terrible practices on your own site, such as pages which require users to click on fake button images to do actions. It makes absolutely no sense how you are "policing" the integrity of your own site and the linking to other parts of the greater web.
Essentially, users who choose not to provide Facebook with their close friends, family, university, and location will be scoped out and tagged by their own friends using these smart lists. It's a disturbing strategy for data collection.