I don't think there's a firm consensus on the reasoning, but it's generally acknowledged that the Sch. 1 classification of the psychedelics was motivated to 1) quell their threat of cultural and political destabilization and 2) to keep hippies and blacks in check. The 60s were similar to Occupy Wall Street: there's major (valid) fear on the part of the establishment when a radically different movement picks up steam. Psychedelics were (rightly) considered a partial fuel to the new movement.

I also agree that the U.S. is much less of a monoculture now and people generally agree that others should be able to live, think, and believe whatever and however they want.