Autonomous weapon systems are no different. They raise the deterrence factor so that you are not likely to be attacked by simply having the capability and your adversary knowing that you have the capability.
This is something i've always found weird... Nukes arguably make the world safer by your definition one but particular country gets to decide who is safe and who gets a free conversion to democracy.
Its maddening.
It depends on who has them and how they use them.
Autonomous weapon systems are (theoretically) much more precise and don't leave radioactive destruction in their wake (unless they are nuclear-armed autonomous weapons systems--that's a terrifying thought).
The greater precision and less permanent nature means they are more likely to be used offensively rather than just held in strategic reserve as most nuclear arsenals are.
What makes nukes unique, and MAD work, is the simple observation known to every nation: if one country decides to nuke another, there's nothing anyone can do about this - once the decision is made and the button is pressed, the other country turns into glass. But since nukes fly longer than the time it takes to detect and launch a retaliation strike, no one dares to launch first because they'll get glassed too, and there's also nothing anyone can do about it.
Conventional weapons, autonomous or not, can't unleash destruction at necessary scale and certainty.
There are quite a few countries that have nukes now, and not just half a dozen little ones. For example, India has SSBNs.