Thumb On The Scale Law

This is something Barack Obama had to say about the Constitutional interpretation as quoted at The Volokh Conspiracy:

I think the Constitution can be interpreted in so many ways. And one way is a cramped and narrow way in which the Constitution and the courts essentially become the rubber stamps of the powerful in society. And then there’s another vision of the court [sic] that says that the courts are the refuge of the powerless. Because oftentimes they can lose in the democratic back and forth. They may be locked out and prevented from fully participating in the democratic process.

I don't want to read too much into what he said (to a highly politicizied audience), but whether you think the proper interpretation of the Constitution should be "cramped" or expansive, is it really a Justices' job, to favor one side or another, the powerful or the powerless (even assuming she can tell the difference)?