Extinction scale events have been "a thing" in Earth's history for as long as Earth's been around [0], as you note we are very likely in the middle of another one right now [1]
The big difference this time being: Previous ones most certainly had not been man-made, this one has a very high chance of being man-made. Who's to say humanity is incapable of damaging Earths biosphere beyond a point where it can recover? If we can manage to fill the oceans with more plastic than fish by 2050, then I'm certain we can manage to do quite a bit of damage to this planet as a whole [2].
A while ago I read a paper reasoning something like that might be the explanation for the Fermi paradox; extraterrestrial civilizations getting so advanced that they destroy the biosphere of their own planet, beyond repair, but not advanced enough to escape said destroyed planet. Sadly I can't find it anymore.
[0] https://en.wikipedia.org/wiki/Extinction_event#List_of_extin...
[1] http://www.theworldcounts.com/counters/degradation_and_destr...
[2] https://www.washingtonpost.com/news/morning-mix/wp/2016/01/2...