Interesting, why are you afraid of it? Should you be more afraid if it wasn't there. Idea behind it makes so much sense. Its main reason for existence is to handle crazy twitchy hands of nervous people at the top of the Soviet (Russian) govt.

The idea is if they think there is an attack, say from a failed sensor, without Perimeter they'll be more likely to press the trigger while they still have time, before they are wiped out and never get a chance to retaliate. With Perimeter, they just activate it, and it will increase the chance of retaliation even if initial attack (presumably from US) succeeds. So in result they'll be less twitchy, more calm and as a result everyone lives happier, longer lives longer on earth.