Actually the pictures aren't racist in their intentions but the photographer appeared to have better success at photographing blacks. The pictures of blacks in regards to whites are disproportionate to the true reflection of poverty in 1975. The pictures are meant to show "Americans don't live as well as the media reflects" type of in your face for their fellow country men. Poverty regardless of the race is sad and needs attention today just as it did back in the 30's, 50's, 60's and 70's. One does not need a camera to know that poverty exists. The actions that are the result of poverty and being an underclass can be seen on news stations daily.
Below is a statement from one of the pictures posted:
This woman reflects the distrust, fear and self-loathing I find in most poor whites in America - one of the hardest groups for me to photograph.
This might explain why there were so many photographs of african americans. Just my .02.