Missile Defense
Missile defense is one of the more challenging concepts within the field of Nonproliferation, as it's totally unintuitive by being total opposite of what people expect it to be.[1] While you might expect defenses to, you know, make you safer, in reality since missile defense has the potential to disrupt the balance of nuclear deterrence, it actually ends up doing the opposite.
While critics of this view will point out (quite accurately since the systems likely don't work very well) that it doesn't actually do this, it's worth remembering that the very potential of being invaded is why many countries have pursued nuclear programs in the past. But yeah, I'm sure if you just tell the Chinese and Russians that this system isn't for them it'll make them feel wonderful about the fact we're constantly spending billions on it.