Because, from my standpoint, even casual sex with a white woman ignores the centuries of oppression she benefits from. It is to treat her as if she is not an active participant in a conspiracy to deny me and my black brothers and sisters the liberty and freedom all human beings should enjoy. Unless, of course, she is one the highly rare whites who openly disavows white supremacy and rejects its benefits, aggressively working alongside black people to overturn this system. As we both know, such a white person is an anomaly if not an outright fantasy, a person so rarely encountered as to be a figment of one's delusions.
I also point towards black women, the self-hate of whom is rooted in society's worship of white women, who are held as the standard of beauty to which all women are judged. As a black man, I find it impossible to ignore the divide between black men and women, this tension fueled by the constant propaganda that seeks to reduce the appeal of black women in our eyes.