Konoar, you are wrong.
What others have noted here needs to be considered. It's not the fact that Facebook is blocking ads that point to google plus, it's that they (apparently) have chosen a particular competitor and applied a completely different set of rules that others are not bound to. That, by definition is anti-competitive. I'm not lawyer, and certainly wikipedia should be taken with a healthy dose of common sense, but these are the first two sentences of the entry on United States antitrust law:
"The United States antitrust law is the body of laws that prohibits anti-competitive behavior (monopoly) and unfair business practices. Antitrust laws are intended to encourage competition in the marketplace."
http://en.wikipedia.org/wiki/United_States_antitrust_law
Antitrust is EXACTLY the same thing that Google is now being investigated for by the department of justice... by promoting an unfair pricing / ranking schematic against competitors by ensuring their own ads are listed higher than those of the competition. (Yelp, I believe).
If I were facebook, would I find a way to stop Google+ ads? You're damned right I would, but I would be subject to the same scrutiny of those who comment here.
This is not a no-brainer. This is a big deal.