The case of Karachi

So, the same Taliban that have no hesitation in shedding Pakhtoon blood all over Fata and NWFP are afraid of Pakhtoon bloodshed in Karachi? To me that does not make sense. Further, as far as I know, MQM and PPP have no overt policy or threat that they will respond to terrorist acts of small groups with ethnic cleansing and civil war.