The whole point of run-off voting in the South was to allow multiple white candidates to run, and if a black candidate wound up ahead, the voters for the other white candidates would rally against the black candidate. (Probably the reverse happened in heavily black-majority districts, but with much less organization.)
As an add-on to your post, I know that some Memphis Democrats were quite pissed off when the multiple black candidates split the black vote in their primary and there was no runoff, allowing white Jew Steven Cohen to win with a minority. The black racists in that district even put up an independent candidate because they refused to vote for a white man.
So if you're going to say runoffs are "racist", something I do not believe because a person should be required to have more people vote for him than against him, then you're acknowledging black racism exists as well, in which case means that at the end of the day it all evens out to a zero-sum game and runoffs are of equal benefit to everyone.
http://blog.washingtonpost.com/sleuth/2008/02/jewish_rep_cohen_battles_antis.html
