It's a great way to end an argument. Just tell the other person that he or she is racist, and that will stop the other person in his or her tracks.
The worst of straw men, the non-issue shuts many people down because they feel compelled right away to explain that they are not racist.
How does one prove a negative?
If I married a black woman, had black kids, attended a black church, some black people would still call me out as racist. It's a standard that can never be met.
The whole race-baiting con is just like the Salem Witch Hunts of colonial New England or the Communist Witch Hunts of the 1940's and 1950's. Even the threat, the accusation automatically makes the suspect guilty until proven innocent. Plus the burden of proving something that is not adds to the complexity and frustration which besets the accused.
No matter how hard one plead before the House Un-American Activities Committee, those arraigned before Congressmen looking for someone to condemn would set up an easy mark for themselves once they implicated or indicted someone.
As for the Salem Witch Hunts, the guilty (hardly just "accused") would endure fatal trials before they could be exonerated. At which point, even if the person was a witch, she could not do any harm once she was dead.
The standard of guilt before innocence, plus the impossible challenge of proving that one is not something offensive or heinous, especially in one's deep-set, far-removed prejudices, is an inexorable crime.
There is another facility where the standard of proof lies in the eyes of the accuser, as opposed to objective fact: a mental institution. The Soviets would imprison political dissidents for an undisclosed, undetermined period of time, until the authorities deemed the individuals fit to be released, a period which would never come for many accused "madmen".
Labeling without evidence, that then demands impossible proof from the accused, initiates a hateful, hate-filled society, bordering on totalitarian.