The absolutely most terrifying horror flick was "The Last Man on Earth" with Vincent Price. Based on Richard Matheson's novel "I am Legend" (1954).
Dennis Weaver may have been a lib, but he was of that generation who knew how to keep his work and his politics seperate. Anyone remember the McCloud episode where he got high on LSD and started hallucinating? Or the one with the guy who thought he was a vampire (with guest star Tom Snyder?)