Censure
I think for a lot of political activities, it's useful to have a group aggregate the people's will. Calling your Senator directly is a good idea... get their staffers on the record and all that. However, when trying to get Democrats to take a stand -- even when it's both the right thing and in their political interest to do so -- can be difficult. It's an issue of overcoming their fear, in which case having an organization pick up the gauntlet helps out a lot.
Also, for what it's worth, the fear among Democrats that standing up against illegal wiretaps (or any of a host of other issues) will leave them looking "weak" reflects not only how deeply lost in the the hall of media mirrors most of them have become, but also the extent to which they are without their own ideas or vision for national security or the US's role in the world. This is a big problem.