Why does Crooks cringes at Curley's wife's suggestion about being " strung up on a tree"

Crooks is black. Slavery and the atrocities committed against blacks in America still fester. Although officially against the law, the lynching of blacks still takes place. Curley's wife need only make up a story about Crooks making a sexual indiscretion toward her and he would be "strung up on a three." There would be no trial or fuss. Crooks would suffer the fate of countless numbers of innocent black men.