Progressives really have to stress the value and beauty of defending the constitution, along with the rule of law. These lay the foundation for a moral and just society, but without having to argue about morality with the right wing. To American society, the validity of adhering to the constitution and rule of law is as unassailable as the validity of "science". Republicans cannot argue against it.
Part of standing for something is to act accordingly. At this point in our history, if we are to observe the rule of law and adhere to the constitution, we are duty bound as citizens to call for the impeachment of GW Bush and Dick Cheney.
This is not an expression of what we're against. If you buy into that argument then you have been spun by the right wing. Impeachment is a necessary step to clear the path for lawful government behavior. Our nation is at risk. If we are afraid of impeachment, and allow laws to be broken and our Constitution to be rendered meaningless, then we fail as a people and as a country.
Impeachment is not by any means the only thing that progressives "stand for", but if we shun it, we stand for nothing at all.