Never mind the Soviets in Afghanistan; look at our own experience in Vietnam for lessons. If the native population won’t fight the war, then there is no reason for us to. Many ARVN died honorably for their young country, but too many South Vietnamese wouldn’t shoulder the burden of the war. Vietnamization failed, and the final nail was driven into their coffin when Dems in Congress cut off their aid.
I think it would have been more punishment for the Soviets if we just let them keep Afghanistan.