^ Thats because Pakhtuns dont take crap from anyone. Be nice to them, they'll be nice to you. You point a gun at them, and they'll point a rocket launcher at you.
There is no bravery being shown by anyone here during these riots. While MQM goons are target killing poor pakhtoons, the criminals belonging to pakhtoon community are killing innocents in mob like sitaution here as reported by one poster here.
But so far more pakhtoons have been killed in target killing so far than other party's people.