If you disiagree with someone, do not put that person on the spot, as this only instigates anger on his part. Educate him by reverse education. Encourage him to question himself and do research.
Have them educate themselves and ask their own questions. Say things like, "Don't just do as I say, look it up!" Or, "Don't take my word for it, look it up for yourself."
If someone says, "FDR was one of the best presidents," and you disagree, don't say, "Fdr was a bad president." That might stir anger. It will stir a natural response, and that is defense.
Instead, state a fact or ask a question. Say, "I sometimes wonder if FDR is such a great President. Unemployment was still high when he left office compared to when he entered."
He'll say, "Is that true?" You say, "Look it up."
The more you try to prove them wrong the angrier and more defiant they become. So lead them to teach themselves. Use reverse education.