^I agree with DNZ here. I would characterize the Soviet Union in a few ways. I would either agree with Hillel Ticktin that it was a "non-mode of production" (neither state capitalist, socialist, etc.) but I could see making the logical step of characterizing the Soviet Union as a Coordinator society. If it was state-capitalist, it was a deformed version of capitalism to be sure.
Anyway, I agree with you somewhat. The Soviet Union did not intervene to "help the Afghans" or anything like that. Afghanistan has always, as the World Bank has noted, a positive pre-war record of cost recovery for key industries and great investment opportunities in telecommunications and energy.
I note this in my writing attacking the United States intervention into Afghanistan but it defiantly isn't a secret and the Soviets took note of this.
I agree, the doctrine of anti-imperialism that is upheld, not just by Stalinists and Trots but from everyone from anarchists to liberals, seems to dwell into "morality" instead of class analysis. While the Soviet Union may have developed the areas of telecommunications and energy, it is unlikely they would have developed the country entirely (this isn't to deny that development of energy and telecommunications can have a huge effect on the development of a country as a whole). The PDP, on the other hand, as a movement that formed on it's own in the country, did have a good potential to modernize and secularize Afghanistan, helping to develop a proletariat class.
I agree with you completely though, upholding a doctrine of "anti-imperialism" void of all class analysis and material conditions would be silly. It seems, though, that when a movement forms on it's own in a certain area it has more potential to develop, etc. than if another nation were to impose it's will on another. That should also be kept in mind.