Why did systems of defense against nuclear missile attack threaten the world?

The fact is that in June 1979, Leonid Ilyich Brezhnev and American President Jimmy Carter in Vienna signed a Strategic Arms Limitation Treaty (SALT-2). This treaty had a flaw, it contained a limitation on the total volume of nuclear weapons and missile technology, but there was not a word about the principles of the deployment of nuclear weapons. In theory, both superpowers could concentrate their nuclear missiles at the most dangerous points in the world without violating the agreed total amount of nuclear weapons. The USSR was not slow to take advantage of this, starting the modernization of medium-range missiles in the right places. Since the parity of nuclear forces in Europe was violated, the West European countries became very worried. They were afraid that America would not be able to help them in the event of a nuclear attack by the USSR, since American missiles are very far away. Then the NATO bloc made a decision (December 1979) to deploy the latest American Pershing-2 and Tomahawk missiles in Western Europe as a safety net.