It's a losing argument. Lose it.
Read "Blacklisted by History" by M.Stanton Evans and "Hollywood Traitors" by Allan Ryskind then get back to me. If you support the US Constitution you ought to be appalled at the way Communists and their fellow travelers burrowed into the White House, Justice Department, State Department and the entertainment industry and had a real influence on post WW II geopolitics. Because Alger Hiss was passing secrets to Stalin at the Yalta conference most of eastern europe spent five decades under the Soviet boot. They lost their freedom that your father and millions of other allied troops had fought so hard to attain.
“Extremism in defense of liberty is no vice. Moderation in pursuit of justice is no virtue.” Barry Goldwater.