>The commies started infighting.
What? 1978s PDPA coup has begun from assassination which was allegedly done with CIA help. USSR didn't have any reason to destabilize the relatively friendly Daoud regime. When shit hit the fan, they simply chose PDPA as an ideologically close force.
I would attribute US with intentionally destabilizing Afghanistan. They didn't want to lose ground in the region, especially after the puppet schah got overthrown in the Iran's Islamic revolution (1978-1979). After the initial Soviet intervention the country was stable for quite a while. There were insurgent pockets in the countryside and cells in Pakistan under ISI umbrella, but nothing seriously threatening.
And DRA had support of the populace (otherwise it wouldn't have lasted 3 years without Soviets), not unlike the current (fallen) Afghanistan government.
>The US didn't want to see the soviets build a total satellite state
So let's wreak total havoc in this state to promote our agenda? Who cares about democracy, prosperity, human life and other ideals which are foundation of the western society if we are to buy into its propaganda? And we certainly will not get bitten back by the created chaos...
>Pakistan who were the ones who fanned the extremist flames
Are you seriously implying that the US didn't know who are they working with in Afghanistan? FYI in 1985 Reagan's government has officially started supplying Stingers to mujahidins. And I am quite sure that CIA has closely worked with the forces on the ground far before that. Also considering that Saudis (well-known democratic states, who had absolutely nothing to do with 9/11) also co-founded this campaign, I highly doubt that the US didn't know really well who exactly they support.
It's far from the first time when the US has supported really questionable forces to get an advantage in the Big Game.