In one sense - facebook becomes a natural monopoly. Back in say 2007/8 I had to log in to both facebook and myspace to see what my friends were up to. Now I just have to use facebook. That is much simpler and easier for me as a user.
That is the way facebook wants it to be but that could change. For now, you must log on to their service, see their ads and be exposed to their new mesmerizing features in order to connect to your facebook friends. The goal of this lawsuit is for applications like Power to be allowed to let users not need to log on to the facebook website to do this.
Maybe now, but a new competitor could do two things:
Be better in some way than facebook (not selling users private information would be an easy one)
Make it so that you could see what you friends were upto on facebook, but without being a user yourself.
Suddenly you cracked the chicken and egg problem, which is exactly why facebook goes after this with the force of the law.
A monopoly based on technology never lasts, but if you can build one on some kind of legal issue, you are golden.
Two big competitors are much better than just one.