The USSR in Afghanistan was a symptom, not the cause. Even if they'd stayed out of Afghanistan, they would have experienced the same collapse, merely slightly later.
It's the same as people who like to claim that the US escalating military spending under Reagan forced the USSR to match spending to keep themselves competitive, which ultimately bankrupted them (thus implying Reagan single-handedly killed Communism). While that ALSO played a role, and helped accelerate the process, the real problems were there long before 1980.
People always like to point to things like bread lines being indicative of the USSR's economy being weak, but it's been established that there were farms in the USSR that were producing so much food that it was left to rot in the fields, because what was actually lacking was the infrastructure to move goods and wealth from one place to another. It was administrative problems more than purely economic ones, or economic weakness caused by military spending.
I think i see what you mean. Though i appreciate that you clarify it. Since i dont know everything hehe ^^