The notion that race mixing can help break down racism shows a very poor understanding of racism.

Firstly, racism is not caused by the fact that different people are of different races. Racist attitudes stem primarily from social conditioning and deep feelings of inadequacy and insecurity. These feelings are projected unto others as persons seek domination to increase their own sense of self worth. In other words, race is just used as a means by which some deal with their own inner turmoil.
Clearly this notion of inter-racial mixing is fatally flawed especially as it may perpetuate the preference of light skinned mixed persons over Dark/kinked haired Black Africans. Also it has nothing to deal with this reality of Dark Africans who have to face day to day abuse often from the white and mixed ones. It does nothing do address the fundamental ignorance that is the essential cause of such attitudes.

Also, there is the factor of white/male sexual insecurity, that for e.g motivated slavemasters to sexually force themselves on African women.

People are free to chose their marriage/sexual partners without interference, but the illusion that race mixing will help end racism needs to be exposed. The intentions/motivations of those that advocate 'no race', 'one love', and inter-racial mixing to reduce racism needs to be examined.