Look we people are nobody to decide on legality or illegality of complex international issues without knowing the full details, just based on pdf documents or literal interpretation of the same. Legality or illegality more often than not derives from context which, I know for sure, you are not fully aware of.
Without 'context' and with the language of the UN Charter/international law clearly debunking the US excuses arguing in favor of legality, the US position is in fact clearly illegal. There is nothing stopping the US from making a comprehensive legal argument in favor of its position and taking it to the UN and asking the UNSC to pass a resolution legitmizing its actions (as called for under Article 51 of the UN Charter), but outside of occasional vague statements, the US is not going to do so because it knows that its legal position is weak and flawed.
So I will restrain myself from commenting on the legality of illegality of drone strikes and would advise you to do the same.
You can do what you wish, and since you have no argument to support the US position or take on the refutation of the US position provided by myself and other commentators, it suits you to try and dissuade people from discussing an issue on which your (US) position is weak and flawed.
Anyway my point was not that - rather why Pakistan has not taken this "alleged" violation to any international fora. It is not because it wants to limit the confrontation with the US or continue with diplomatic engagement - as things like the continuous feeding of anti-Americanism in media or the posture taken by the Pak politicians to the domestic constituency is in direct contravention to the supposed desire to limit the confrontation or work out mutually possible solutions.
The explanation for not taking it to international for/shooting down drones, remains the same - a lack of desire to escalate the situation. Your analogies (feeding anti-Americanism etc.) don't fit, given that the neither the GoP nor the Military institutions have done any such thing officially, and claims to this effect are mere speculation. In any case, the anti-Americanism' in the Pakistani media is no different that the 'Anti-Pakistan propaganda' in the US media, supplied by the US 'Deep State'.
A decision to take the drones strikes to the UN/ICJ or to shoot the drones down, however, will be the result of an official and explicit GoP policy decision, and hence the escalation in relations with the US will be significant compared to the speculative scenarios you painted.
It is because it knows that when it approaches any higher international institution then there are many skeletons in its own cupboard that would come tumbling down and would ultimately end up embarrassing itself than the US. So while taking a honor brigade stance to the Pak public, who dont have access to the full details and just lap up what appeals to their sense of patriotism and honor, the tacit approval to the drones from Pak is always there.
There is not skeleton that will come out of Pakistan's closet that has not already been discussed in the media and that the US has not already tried to manipulate and arm-twist Pakistan with. If there were any such skeletons, why has the US not already trotted them out, given that it is at the supposed 'end game in Afghanistan' where it needs Pakistan to 'tow its line' as much as possible? As with the rest of your post, this is just more speculative balderdash. Pakistan's legal position based on the UN Charter is very strong, for reasons already explained several times.
Bottom line - unless and otherwise Pak approaches any international institution will all relevant evidences, materials [gathering which should be very easy considering that you yourself have "proved" that they are illegal] which show that the drone strikes are illegal and are in contravention to international norms, the line that the drone strikes are illegal - is just the Pakistani narrative and there are not much, if not any, takers in the international arena for what Pakistan has to say.
Pakistan does not have to gather any 'evidence', Pakistan has to merely point out that
1. There is no UNSC Resolution authorizing unilateral military action by the US inside Pakistani territory
2. Articl 51 of the UN Charter clearly places limits and conditions on military actions taken under the guise of 'self defence' by one State against another State
3. Pakistan has proposed multiple feasible alternatives to make the drone strikes or any other military operation on Pakistani soil a cooperative measure, which debunks the US Self Defence argument.