When Barack Obama ran a campaign with a slogan he borrowed from Cesar Chavez and the United Farmworkers, Yes We Can, and preached his gospel of hope, he was tapping into a long progressive tradition dating back to our very founding as a country.
While righteous anger and cynical humor are an important part of our work, progressivism that is at its core cynical and pessimistic doesn't work over the long run. For one thing, it will burn itself out. When I was a young organizer being trained, I was told that you can't organize people if you are too depressed to be hopeful, that if you were feeling burnt out, you should take a vacation or even get into a different line of work. I still believe that to be true. Righteous anger is a great thing, and can feed you for a while, but if it's not leavened with hope, it won't sustain you over the long good fight. But it also doesn't work because the internal contradiction is too great. Telling people that we can change things for the better while being cynical about any hope for change is a self-defeating philosophy.