Of course, if enough people decide to leave G+ due to them (which I doubt), these rules might actually becomes themselves bad for their business.
But would they have to? I mean, Google's whole business model is to match ads to the right content, and they specifically say they're good with detecting such "offensive" images, so they could simply content match advertisers who were looking for "edgy" images.
In which case, if a website has a comments section or other area where users can interact with one another, should that area be a "public" place, and allow free speech etc.?
Addition: since the purpose of free speech law is to allow anyone to say things that may well not be liked by an authority figure, companies being censors could act as a surprisingly effective loophole to free speech law. Just make all methods of communication between citizens pass through a company, who handles the censorship, leaving the tyrant free to go about their day.
As for your addition, to make all methods of communications pass through a company would either require a law, which would be unconstitutional, or would require more insidious methods. The government already has plenty of insidious methods of dealing with people.