~When America armed the Mujahadeen in Afghanistan with anti-helicopter missiles the Russian invasion of Afghanistan came to a bloody, grinding halt.~
It is largely a myth. Soviet aircraft losses were minimal comparing to Vietnam, let alone manpads weren’t all that effective against their choppers. No more than 20 helicopter gunships were lost to Stingers.
And I don't want to make it seem as if just one weapon type added to a campaign acted as a silver bullet. Operation Cyclone was based on a broad base of weapons, tactics, and logistics.
But Wilson (the congressman behind Operation Cyclone) described the first Stinger Mi-24 shoot-downs in 1986 as one of the crucial moments of the USSR/Afghan war, saying:
"we never really won a set piece battle before September 26, and then we never lost one afterwards".
He might have had an axe to grind of course. But helicopter mobility was critical to the Soviet battleplan (e.g. for deploying toops and landmines). Anything which increased the range of shootdowns must necessarily have circumscribed Russian strategy.