I can see some pessimism in it, too. Humanism allows us to be free agents, for sure; but exactly how much freedom and control do we have? In that way, it's more optimistic to believe that we have a higher power on our side that will help our environment give it the nudge it needs for us to press it forward.
Free-will and mind-body dualism (if it isn't... explain beer?) is an illusion. Nevertheless I think political liberty is important. I consider myself a humanist, if not always an optimist. However, I'm in an optimistic frame of mind as of late.