There was too much oxygen at one point when there were only plants breathing. As a result, life developed that removed the toxic and flamable Oxygen from the plant environment so that the life would stop catching fire a la planetwide forest fires.
I think that what the people who argue against fixing the climate issue don't understand is that the planet will continue with or without Humans. Just because we render it hostile to oxygen breathing life, does not mean that other life wont come along and take advantage of that niche.
I would prefer the human race not have to dissapear for the planet to fix itself this time. That is a destiny we have the technology to stop. However the political and financial will is not there to stop it anytime soon, and frankly, time is running out.