I have been reading Sorrows of Empire by Chalmers Johnson, and one of the things that stuck me was a quote by Soviet hydrogen bomb creator Andrei Sakharov who was released from political imprisonment by Premier Gorbachev in large part to analyse the Strategic Defense Initiative. SDI was a massive military research program to develop a missile shield to render Inter-Continental Ballistic Missiles obsolete. After the fall of the Soviet Union many of the project's supporters and conservative supporters of Ronald Reagan claimed that the policy was largely responsible for initiating an arms race which "broke the back" of the Soviet Union.
However, it seems that the Soviets really didn't consider SDI much of a threat, in Sakharov's words,
"An SDI system would never be militarily effective against a well-armed opponent; rather, it would be a kind of 'Maginot line in space' expensive and vulnerable to counter-measures. It would not serve as a population defense, or as a shield from which a first strike could be launched, because it could be easily defeated. Possibly SDI proponents in the United States were counting on an accelerated arms race to ruin the Soviet economy, but if so they were mistaken, for the development of counter-measures would not be expensive." (emphasis added)
Also from the same book by Johnson, "...according to Anatoly Dobrynin, the Soviet ambassador to Washington, as early as February 1986 Russian president Mikhail Gorbachev concluded that,'...to destroy or neutralize the American SDI system, we [Soviet Union] only would have to spend 10 percent of what the Americans plan to spend.' ". Also according to statistics presented in the book the Soviet spending on weapons procurement dropped from 4 to 5 percent to 1.3 percent per year and that Russian appropriations for offensive strategic weapons declined by 40%.
I have long believed that the USSR fell due to reasons outlined by Chalmers, that being that, "The USSR collapsed for three basic reasons-internal economic contradictions driven by ideological rigidity, imperial overstretch, and the inability to reform". What I want to know is if there is a counter-argument, based on legitimate evidence, that supports the claim that SDI did indeed significantly contribute to accelerating the fall of the Soviet Union?