That's exactly what they are doing, if they were genuine in getting rid of crime and violence in Karachi then they would be doing raids all over Karachi, there are no go areas in Karachi where Taliban are hiding, they keeping low profile for now because of military operations, but they will be back under a new banner of ISIS. Maybe Rangers are cleaning Karachi from any armed resistance against future ISIS take over of Karachi. Without Karachi the Islamist revolution cannot succeed in Pakistan. Karachi is the life line Pakistan so they have to clear Karachi of any liberal or left leaning forces from Karachi.
MQM is the only political party that is willing and has the capability to fight back Taliban in Karachi, that is the reason why establishment hates MQM and Karachites.
Degrading MQM's power will only backfire. If MQM goes underground, Karachi will have a nightmare to deal with. Talibunnies will come out in open using different names and Rangers will not protect the weak.