Why destroy all nuclear warheads and atomic bombs as quickly as possible?
These weapons are not usable, very dangerous to maintain and handle, very costly, and have an adverse effect on foreign policy/world peace.
These weapons literally cannot be used for furthering any military or diplomatic gaol as they create wastelands. They unselectively target children, mothers, fathers, families - since their first use, no civilized nation can ever use them again.
In diplomatic negotiations they have an intimidating effect and present a hindrance to a trust building process. For example, there would be no reason for North Korea to develop nuclear weapons if the United States had none.
http://www.projectcensored.org/occupying-the-merchants-of-death/
read "Getting More" by Stuart Diamond