Creating a Darwin Day as a national holiday would be a really bad idea. The public promotion of darwinism by scientists has confused the issue between evolution and darwin’s theory of natural selection, the latter exposed many times. To enshrine this set of errors when the larger community is moving past darwinism would be a major error, and the source of endless future conflict with Congress as a bunch of muddleheads following the advice ad infinitum of propaganda orgs like the NCSE.
Beyond that the real discoverer here, Lamarck apart, was Wallace, not Darwin. The whole idea here is entirely ill-advised.