It's All About Factions
After the killing of Bin Laden, there have been a lot of questions about how much the Pakistani government knew about the situation. One thing to keep in mind is that Pakistan's political environment is riven with factions, each with its own agenda and armed supporters.
For example, from one of the latest Wikileaks cables:
"MQM's armed members, known as "Good Friends," are the largest non-governmental armed element in the [Karachi]. The police estimate MQM has ten thousand active armed members and as many as twenty-five thousand armed fighters in reserve. This is compared to [Karachi's] thirty-three thousand police officers."
MQM is a Pakistani political party.
Factional struggle is something that is prevalent in many governments and large organizations; it means that there may not be one single organizational policy. When viewing events as an outsider, it's important to remember that we see is the result of factional struggles, in which any group's dominance may only be temporary. When the factions are all armed, then, the potential outcomes are potentially more lethal than otherwise.