The consensus is that given enough time every civ that discovers the H bomb will eventually destroy itself.
Just every nation possesing H bomb and using them will not make humans extinct. There will allways one or ore groups would survive in remote islands or mountain caves, could start civilization on a short order, becaue humans will add on existing knowledge and this knowledge is progressed in exponential order. The real danger is in bioterrorism. For nuclear research and cheical weapons need large infrastructure and personnel. Even if one system is perfected only limited to some kind of boundaries. For example a Hiroshima type bomb would destroy say quarter or half of Manhattan Island. Very large one will destroy e few islands of Nw York City.Other places peope suvive The chemical weapons cover a less area of destruction.
But for Biological terrorism one does not need big infrastructure, instead 3 or 4 people in a very small laboratory can make this weapon. We have all seen what 4 letters laced with antrax caused the kind of panic. Imagine instad of 4 lettrs they sent 4 thousand letters in all directions, The person who sent 4 letters obviously did not want to kill himself. But if a group of people want to die and spread it can cause 100 even thousand times of destruction.
I did not imagine the destrucive power after the anthrax attack, but long before when I had rudimentary knowledge of molecular biologyin yhe mid sixties, Now what would happen if somebody sent 10,000 anthrax letters with geneticall altered organism, whrere the known antibiotic will not work. An doing those are not that difficult.