MLK was against anybody promoting racism. I'm sure he also took issue with Jesse Helms and his father (both Republicans as far I know).
Truth is MLK had another side, a side that wanted to declare a war on poverty. He felt the way to go after poverty was through socialism. I don't think he was this hard ass socialist that Lenin was, but he was at least social Democrat like (excuse me for using the word "Democrat", but I don't know what other term to use). The same guy also stood beside Margaret Sanger and praised her (considered a liberal today, although I sometimes don't want to claim her).