Publius explains:
To rid ourselves of the Cheney worldview, there has to be a political fight against it a final showdown. A game of chicken. Rank-and-file Dems need to know that their alternative worldview (no torture, rule of law, etc.) are politically viable. Every time one of these issues comes up, vulnerable Dems will rightly fear juvenile ultra-nationalist attack ads that is, until the Dems stand, face them, and win.
Shorter version:
You must confront Vader. Then, only then, a Jedi will you be.