Person A says "He's a racist!!"
Person B says "I don't believe it"
Person A says "How dare you defend a racist!"
I say "So by saying that I don't believe an accusation that someone's a racist, according to you, then I am an advocate for it?"
Person B, if answering honestly, would say "Yes" because it's clear that's what they believe.
Now insert any other accusation in place of "racist" and that's what many of us face on a daily basis.