The alliance with the United States has allowed South Korea to build a strong democracy with citizens confident Washington would protect them if North Korea ever acted on its dream of unifying the peninsula under its own rule.
Nuclear weapons in the current era of mutually assured destruction are strictly a deterrent, only useful in a hypothetical retaliatory strike but not as a realistic offensive weapon. The hypothetical situation where this would hypothetically be used would be after Seoul has fallen to the enemy and defeat is inevitable. By having such an ability, this makes it very unattractive for any enemy to try to conquer and fortify Seoul or put any existential pressure on South Korea by any means, since doing so enables the use of a retaliatory nuclear strike, since in such a hypothetical situation there is no chance of regaining Seoul left for South Korea to worry about. Therefore, as a consequence, Seoul is protected in a very material sense by a weapon that will never have to be used in any actual strike ever.
They may only be a deterrent but they continue to be an extremely convincing and effective one.
Nuclear weapons in the current era of mutually assured destruction are strictly a deterrent, only useful in a hypothetical retaliatory strike but not as a realistic offensive weapon. The hypothetical situation where this would hypothetically be used would be after Seoul has fallen to the enemy and defeat is inevitable. By having such an ability, this makes it very unattractive for any enemy to try to conquer and fortify Seoul or put any existential pressure on South Korea by any means, since doing so enables the use of a retaliatory nuclear strike, since in such a hypothetical situation there is no chance of regaining Seoul left for South Korea to worry about. Therefore, as a consequence, Seoul is protected in a very material sense by a weapon that will never have to be used in any actual strike ever.
They may only be a deterrent but they continue to be an extremely convincing and effective one.