I think the word responsiblity here is still Sagansim. We are not responsible. But, Gia spun an interesting creature that calls itself "intelligent."
So, if somehow there begin an hypoxia event, it won't be us that did it. And we are smart enough to get O2 out if the crust if we have to. So, take the long view.
Saganism proposes that man is a weak link, that man can fuck up a billion years of Gia's work. I don't think so. Saganism is Hubris. The Gia System farted and then O2 favored aerobic activity that spawned the mind of humans. But, that same mind will never give up.
We can make our own O2 for a few million people if it ever came to that....but, not for 10 billion, see? But, we are not a destructive force. The space rock with our name on it is THE Problem.
And if Gia knows anything, she knows that. She has to get the DNA out of gravity well and she is doing just fine on that task. But, it may be a near run thing.
That little ole rock that blew up over Russia this year was not that big, but packed a wallop that made Hiroshima look like an firecracker.