If every gun fired backwards I'd be a huge proponent of guns. I am not for innocent people dying.
As far as mass extinction: I wouldn't be surprised if it happens in our lifetimes. Climate researchers have long warned that if the tundra starts to melt, it will release a huge amount of greenhouse gasses, massively accelerating global warming. This year 2 million hectares of tundra caught on fire.
The single biggest cause for global warming is overpopulation, but lowering birth rates isn't something that has even entered public discourse. I don't think anything significant will happen until human mass extinction is well underway.