Humanity as a species won't end due to climate change. That's a ridiculous assertion. Full scale nuclear war probably couldn't wipe us out completely. Global warming can't either. Billions might die, but humanity will survive almost certainly.
People are very bad at estimating the probability of catastrophic events. We base our estimates on things that have happened in the past, but that doesn't help predict things that have never happened before. Hundreds of millions of years of pent up carbon have never been released into the atmosphere over the course of a couple centuries before. It is hubris to the point of suicidal to think anyone can predict the effect it will have on a complex, nonlinear system like the global climate.
Sure, maybe it will be fine. But the burden of proof should be on the people claiming that it's going to be fine, not on those recommending caution before screwing with something we don't understand.
The gamble we're making is that we're smart enough to survive in the most dire conditions.
That's a stupid gamble, but we might win. Plus we're on a roll so far.