I think it's more that King has always been contemptuous of conservatives, who he views as crazy religious fundies, "Carrie White's mom" types always trying to cram Jesus down everyone's throats.
The thing about these people is that they've never seen true brutal Leftism in action. They weren't living in Cambodia during Pol Pot's regime.
There is that, for sure. There’s also the arrested development of many people who were college and high school students in the ‘60s and ‘70s and still think of Republicans as “The Man” keepin’ ‘em down, and Democrats as the “cool people” who won’t interfere with their yen for sex, drugs and rock ‘n’ roll. There are MANY of those types out there, and no evidence to the contrary will ever sway them.