While Soviet Union was a closed country, that didn't allow terrorists to come into the country. The country was really safe. Since no one actually knew all the truth about the outer world, world outside of Soviet Union, people for not even know the horror, terror, etc. Soviet Union was a safer place than any country right now. And even the Cold War, it was cold, and really not even a war- it was more like a challenge, determining who is better.
The Soviet Union made the world a safer place in their own neck of the woods, which spans two continents. The Soviets had to make sure they many different groups of people with deeply contrasting backgrounds did not start wars with each other. Muslims, Christians, natives, and skin heads all had to live under one place. That meant peace-keeping by Soviets.
Actions by the Soviet Union have made the world a safe place to live. By standing down its stock pile of atomic warheads it ended the tensions with the United State, that had the world in a state "Cold War." By becoming a responsible member of the world community the Soviet Union has helped to create a more stable state of international affairs and a safer planet.
No, the Soviet Union did not make the world a safer place, because the USSR was always on the brink of war. The United States made the world a safer place by being strong enough to fight it. All of the countries that fell to communism were not safer for it. The USSR would have taken over the world if the United States wasn't there to stop them.
The Soviet Union was a massive communist dictatorship and all of the nations within were at odds with one another. That was a very dangerous and unstable union, and it is good that their economy eventually failed and that America got them to back off of their idle threats. They were dangerous.
I do not believe the Soviet Union made the world a safer place. If anything the Soviet Union helped make the world more dangerous by entering an arms race with the United States. The results of this were the most destructive weapon ever created by man. A country can't do that and make the world safer at the same time.