In the Introduction to Law of Peoples (1993), John Rawls claims that as a consequence of focusing on the idea of a realistic utopia he will leave aside discussion of issues in foreign policy, particularly "unjust war, immigration, and weapons of mass destruction." But he does give a low key argument toward the end of the introduction (p. 9) about keeping outlaw states in check by the threat of possible nuclear attack.
[S]o long as there are outlaw states - as we suppose - some nuclear weapons need to be retained to keep those states at bay and to make sure they do not obtain and use those weapons against liberal or decent peoples.
The idea here seems to be that countries with nuclear weapons capability need to hold onto these weapons as an insurance policy for outlaw states manufacturing or creating their own nuclear arsenal. The assumption is that if nuclear superpowers, such as the US and Russia, have nuclear weapons, then outlaw states will think twice about acquiring them for fear of retaliation from either US or Russia.
Events, since Rawls' book was published in the mid-1990s, have proved his view at least somewhat incorrect. Retaining nuclear weapons against rogue states do not act as a deterrent from them attempting to acquire the capabilities of producing nuclear weapons. In fact, it seems to further embolden them to build their own nuclear arsenal. Think here of outlaw states like North Korea. Despite the strong alliance between the US and South Korea, North Korea continues to develop its own nuclear power capabilities. It even regularly holds well publicised exercises in which ballistic missiles are launched into the Sea of Japan as a means of showing the US and Russia that they are developing their nuclear arsenal.
Granted, outlaw states have not always had the hutzpah that North Korea has. Outlaw states have often used alternative tactics in their fight against nuclear superpowers, e.g., guerrilla warfare, ambush, sniper, and with some great effect. They use these sorts of tactics because they know that they cannot compete with the more technologically advanced weaponry of the nuclear superpowers. If they know they cannot win in terms of technological superiority, then they revert to unconventional tactics in a ground war.
The assumption that nuclear superpowers will be able to deter outlaw states from developing or acquiring nuclear weapons seems deeply flawed for two reasons. First, it seems that such countries like North Korea continue to develop a nuclear arsenal in spite of the threat that their neighbour, South Korea, has the support of the US government. Nothing has deterred North Korea from developing these weapons, and they certainly don't seem enthusiastic about letting UN peacekeepers inspect their nuclear facilities. Second, if an outlaw state decides not to develop a nuclear arsenal, then they may just revert to alternative unconventional tactics of war to beat their technologically advanced adversary.
So, even if liberal or decent peoples retain a large cache of nuclear weapons, it does not keep rogue states (or terrorists) at bay. The outlaws find new and interesting ways of fighting the super power. They use tactics the super power is not equipped to handle very well.
I think the argument could be made that if liberal or decent peoples have a large cache of nuclear weapons, then outlaw states will have more reason to obtain these weapons of mass destruction, more generally. Large caches of nuclear weapons are a threat to states that do not have them. So, they have reason to seek nuclear weapons for their protection.