He's not. This is Jeffrey Sachs's view of what he thinks the Pope ought to be saying, not what the Pope actually is saying.
The relationship between freedom and virtue is something people have been discussing for hundreds, even thousands of years. The answers are a lot more complicated than what Sachs wrote (or than what any of us can come up with on the spur of the moment).
Ah, nevermind then. Large brain fart from me in that case.