Though I would state the people saying the US has NO reason to do it are being pretty ignorant.
There is plenty of reason to do it... it's not like Obama is going "Hey lets send a bunch of troops and drones into Pakistan for the hell of it."
They're sending troops in to take out militants that openly attack and make plans to attack the US and often Pakistan.
The question is should US security trump Pakistani sovereignty when Pakistan's responses appear to be slow and may even involve tipping off said groups before security teams arrive.
I'd say "Not really except in EXTREME cases" and as such the mass escelation by Obama is ridiculuous. (I believe an administartion official is quoted as bragging that they've had more drone attacks in pakistan then the entire Bush presidency).
To say they have no reason to though is just.... dumb.
