I think that's exactly the point: why limit the analysis to racist speech (when the idiocy hurled on one side will be racist) and not equally bad - or worse - speech (when that other type of speech is on the other side).
It's sort of like tracking all the cases of food poisoning from pizza and ignoring the food poisoning from fish.
"Hey, I've got data that says that people get poisoned from other foods too."
http://twitchy.com/2012/11/06/death-threats-against-mitt-rom...