One of the core problems with the progressive movement is that it fails to accurately understand human nature. A core tenet is that humans are perfectible, and it is only through progressivism that humans can attain this perfection. Yes, progressivism is a replacement for religion, or the attempt to do so.
But humans are actually subject to human nature, and debase, or sinful creatures. Thus, so many progressive ideas become derailed by their inane desire to believe that the good works of progressivism are sufficient to lead people to salvation through progressivism.
Human nature reigns, and will continue to do so indefinitely. Perhaps we will eventually break free from the grasp of our long evolutionary/God instilled history which has created our human nature, but not in the foreseeable future.
Even disregarding all of the other good reasons to leave progressivism in the dust bin of history, this reason alone is sufficient. We cannot move forward until we do so. Get to it.