[Bernard Marx]

Douglas was an entertaining actor, but he he took the lead in allowing the communist Hollywood 10 to be accepted in society again. He's always been a UN activist and his son has inherited the mantle.

Yup

His movie "Spartacus" was based on a book by Howard Fast, whose Communist past got him blacklisted by the Hollywood studios. Dalton Trumbo, another blacklisted writer, worked on the script. Douglas was considered responsible for fighting to make sure Trumbo got screen credit under his own name.

Fast and Trumbo saw the Roman slave revolt as an allegory for Communist revolution: an inspiration for the revolt of the proletariat against their bourgeois "masters." That symbolism was mostly lost on American moviegoers, and probably Douglas too. He was likely doing the fashionable Hollywood "thing" that remains in vogue among not-very-bright members of the pampered acting class.

This letter written by William F. Buckley about Howard Fast is interesting IMO: Howard Fast

[Borges]

I think it was fairly well known at the time. Hedda Hopper and John Wayne told people not to see Spartacus. The Communist admiration of Spartacus comes from Karl Marx who regarded the historical figure as one of his heroes. The initial crack in the Blacklist came not from Douglas but from Alfred Hitchcock who hired the blacklisted actor Norman Lloyd to work on his TV show in 1957. Lloyd is still alive at 95.