>Tracking them until they hop on a plane
That sort of approach gets tried from time to time (e.g. the ATF's "Fast and Furious" program) but it has problems of its own. What if they never get on a plane? There are US facilities they could bomb without ever going airborne. What if you lose sight of them? The political risks are nearly the same as ignoring the problem. If they were able to kill US citizens, the headlines would invariably read "Government had killer terrorists in sights, didn't pull trigger."
>International pressure
Sure, the US has to weigh the impact of its strikes on global opinion. That's a big reason why we care about collateral damage at all. You bring up trials, but still haven't provided a reliable avenue for terrorists to be arrested.
>Might makes right
You're not doing a very good job of looking at this from a Pakistani perspective. As a Pakistani, my life would be threatened by drone strikes and Pakistani terrorists. You seem to think that it should somehow be my right to try and attack the US government to stop the drone strikes. That is childish reasoning, military conflict is not some sporting event where the rules try to create a level playing field. The US has the means to target terrorists, but I would lack the means to target the US drone program. I could try, but any damage I could do to the US would inherently be indiscriminate. At best, I would end up killing some innocent Americans and their government hunts me down, at worst I just get my family killed in a drone strike. What are my other options? The most obvious one is to personally organize my friends and try to root out the terrorists that live near me. Then there will be no terrorists to bomb me, and the US will have no reason to send in drone strikes.
Remember, the only reason that the US is resorting to military action is because there is no organization within Pakistan that can be counted on to eliminate the terrorist threat.
>Human rights
Prove the civilian deaths were malicious and not simply collateral damage. I don't think anyone can. If it were possible to demonstrate that a specific drone strike deliberately targeted civilians, I have no reason to doubt that the person behind that particular strike would be held accountable.
There is also the issue of terrorists using human shields. If terrorists knew that the US was averse to any collateral damage, they would immediately become nearly invincible by strapping babies to their chests or otherwise surrounding themselves with innocent people.
>Pakistani v. Pakistani violence.
I didn't know terrorist organizations had to choose between domestic or international terrorism when they write up their charter.