How the McCarthy blacklist annihilated the Hollywood left

It tried to, not sure it did, though it did destroy many careers and drove many people into hiding. But within ten years of the McCarthy witch-hunt black-listed screenwriter Dalton Trumbo was winning an Oscar for SPARTACUS.
And let's not forget that when Lucille Ball was accused to being a "Red", Desi famously replied, "The only thing red about her is her hair."

There are plenty of outspoken leftists in Hollywood.