Sorry bro.
This USSR needing access to warm waters one is such a lame theory. One just has to take a look at the map. USSR already had access to warm waters of Black Sea. Why would it need to come all the way down to arabian sea?
I have question to you...
1. If USA not supported against Soviet then do you think that Pakistan was alone fighting the war with the help from few muslim countries?
2. Isn't Pakistan and india having border issues and there is no officially defined borders.. Still both countries do claims other parts?
3. There are many borders disputes around the world. Pakistan was not facing something unique challenges at western border.
The facts is Pakistan joined the war against soviet because there were several political reasons and opportunities by supporting to USA. Even Pakistan had enjoyed a positive relationship with USA during the time by getting dollars and military equipments.
Thanks for your feedback mate. Let me try to explain.
1. You need to look at Pakistan/Afghanistan border from historical point of view. During British Raj days or even before, this whole area was under constant conflict. Interestingly, the British never assign any name to this region, they called this region North West Frontier Province (NWFP). Perhaps a cursory look at the history of Durand Line would you provide you enough context.
2. If I remember correctly, President Carter's National Security Advisor Zbigniew Brzenzinski once mentioned that the U.S. start backing and funding opposition groups back in the early 70s against the communist Afghan govt to start the insurgency with the aim to drag Soviets in the conflict. So, U.S involvement was there from the beginning. Without U.S, there would be no involvement from Pakistan or any other country.
2. India and Pakistan's LoC situation is completely different. There was no LoC prior to 1948 and both the countries shared international border.
3. Again, you need to look at the history of Durand Line. Lack of any credible central government in Afghanistan in all those years is the biggest hurdle in resolving the conflict.
Here is another side of the story, even way before Afghan conflict, Afghanistan was safe haven for all criminals, murderers, kidnappers, smugglers, car thief etc. Every child kidnapped from anywhere in Pakistan or every stolen car ended up either in the tribal area of Pakistan with strong links to Afghanistan or Afghanistan. Every drug, illegal guns, electronics and other luxury items were smuggled from Afghanistan to Pakistan. Rice, wheat and other products were smuggled to Afghanistan. These are some of the small observations but it will give you an idea. And I must say, you Indian's should thankful to Pakistan that it creates a buffer between Afghanistan and India otherwise things would be quiet messy for you guys.
One more thing, the administration and integration of our tribal areas (FATA) with the rest of the country is also linked with the resolution of permanent international border issue. This single issue has caused so many problems for the government over the past seven decades.