The truth is that nuclear arsenals can provide security in fear of the concept of "mutually assured destruction". Nations do not want to destroy themselves or the species in general, however it must be noted that this is strictly based on REGIONAL security. Global security is an entirely different matter.
Possessing any types of weapons indicates that we are ready for a war. Even though they are meant to defend ourselves, usage of weapons harms other human beings. It is same in the case of nuclear weapons also. If no country in this world initiates a war, then security and global peace will be obtained.
The cold war are examples of how much regional instability it caused. Due to the presence of nuclear weapons in one country,other countries feel threatened and thus leading to a brutal arms race between the two.Therefore i do believe the nuclear weapons are a threat to both regional and world peace.