I see it differently. On the long trend human society is vastly improved. At least in the sense that Marx was talking about, the enlargement of human development. That is the real backdrop to human existence. There it seems to me that Marx's idea of progress is not an ideal, but a reflection of the real development. What you are talking about is a peculiarity of intellectuals, pessimism. The mass of people remain stubbornly optimistic (partly out of a misplaced patriotism, partly because that corresponds to their actual experience).
What the left (if you will permit that broad abstraction) mistakes for a decline in the conditions of human existence is not at all that in its totality, but one particular and important strand. The real grounds for pessimism are the closure of political possibilities, and the demobilisation of mass participation in public choice. That is a real problem (and one good reason to feel optimistic about the Obama moment). The left too often takes its own decline as evidence of the collapse of human civilisation, which, in truth is a lot more robust, and even, let's say it, going places.
I see a lot more to be optimistic about. The challenge is to translate the broader advances in human society into a specific political movement to take control of its direction.