Not sure why you are so offended? Pakistan has legitimate conventional defence needs. Can you deny this? Any major conventional weapons purchase is being funded by Pakistan and not from US aid. Aside from a limited number of EDA articles, most of the major weapon systems including F-16 blk-52s, JF-17s, Erieyes, ordnance etc. has come from Pakistani money. The same as India will be financing the MMRCA, C-17, C-130, M-777 purchases. So not sure what irks you so much? The problem here is the Indian insecurity and that too a massively misplaced one. While, as per your side, no one should ever say anything to India about where from and what they buy, you have no qualms about complaining when Pakistan does the same. Why the double standards? Do you see us complaining when you acquire US, Israeli or Russian hardware? No we don't. Its your right as a sovereign nation to do so, how we manage our defences, you should leave to us in line with mutual respect for each others sovereignty.
What should stop Pakistan from purchasing F-16s for its needs if the Indians are being allowed to purchase the same with Pakistan in their mind as the primary threat or even if Pakistan is not in their minds (this is a big if)?
In military terms, the lower the conventional capability, the quicker up the rungs you go to nuclear escalation. NATO-Warsaw pact never had conventional parity. The Warsaw pact countries always had more. However the Soviets knew that their conventional superiority was pretty much irrelevant because of the nuclear escalation that would take place if NATO suffered serious set backs conventionally. Pakistan's situation is no different. Its a matter of Pakistan's survival. It would be war-mongering if we threatened India with a nuclear strike as soon as things flared up. This is not the case. Pakistan spends money to maintain sufficient conventional capability to avoid having to ever go down the path of a nuclear escalation. Pakistani nuclear weapons have *NEVER* been readied for use despite the trash that has appeared in the press about the 2002 standoff. Realize that people in Pakistan also want to live and let live. India is not on our minds all of the time, however our security imperatives are as such that we require a certain conventional capability to be maintained. If the US side understands this, its all the better for the region.
You seem to be forgetting the point I made about US allowing Pakistan to acquire enough, but not to the point where we attain full conventional parity with India, at least with US equipment. Secondly, nobody is suggesting here that Pakistan should go the path of attaining parity with India conventionally. Pakistan needs to have a "minimal" credible conventional and nuclear deterrence. The US side realizes this and before your insecurities get the better of you, do realize that this is good for India too.