Yep. If I'm going to be intellectually honest, I've given the same pass to Gene Rodenberry and Rod Serling. One of the tenets of progressivism is that human evolution can be guided to improve or perfect human nature. I suspect that having witnessed the horrors of WWII many of them embraced the hope that mankind could do better, and would gravitate toward political and cultural movements that promised a better world with better people.
It would be a natural, though IMHO, naive reaction. The, "human perfectability," hope of progressives largely gave rise to the eugenics movement they were fighting in the first place, and it still lives on more insidiously in the abortion and euthenasia movements.
Contrast all that with the more conservative worldview of Jimmy Stewart who lived firsthand the airwar over Europe. Not long after the war he made, "Rope," with Alfred Hitchcock, which was based on the real life story of Leopold and Loeb, who thought their intellectual superiority gave them an ubermenschian privilege to kill their lessers.
The late singer Tony Bennett was very liberal. He was also an infantryman, and a veteran of brutal house-to-house fighting as the US Army pushed into Germany. Bennett later said that the experience turned him into a pacifist and a liberal.
I respect that.
Nevertheless, you make a very good point. The Democrat Party of the old days has morphed into something very ugly.
I have older friends and relatives who just can’t see that. They still think it’s the party of JFK. So they still vote D. Could Van Dyke and Bennett be in that same boat?