The fact that the only reason America did not go to war with Russia in the 20th century directly is because they were both afraid of the others nuclear capability. Or in the modern day why China shows restraint when dealing with Taiwan because they ultimately don’t want a hot war directly with another nuclear power. Nuclear weapons aren’t great and cause mass devastation obviously but they have kept the major powers from fighting each other directly which would cause way more devastation.
The fact they haven’t already should give you some assurance. Nuclear war benefits no one so the only way one country ever thinks of using one is if they are going to be completely defeated. Though this situation is very unlikely as nuclear powers don’t find themselves weak enough to be caught in that situation. This is why nukes shouldn’t be in every country, but why they should exist as a deterrent for wider conflict.