(CO is much more reactive, but it's harmful to us because it reacts to our hemoglobin in much the same way as oxygen. So since Earth life has managed to get on just fine with all this corrosive oxygen around, the same argument may still apply.)
EDIT: "Especially in combination with water vapour in atmosphere - it would freeze, static charge would build up between the ice particles and the discharge would ignite everything. Indeed the fact that O2 is so high is a proof that there is nothing left to burn"
The fact that there is excess of a reactant really means that there is an ability for interesting reactions, and therefore life. Ash cannot be animate because it’s (basically) at ground level and does not have the free energy to do anything.
I swear, this is an exact line from a Ray Bradbury story that I read as a child.
Of course, that's a completely different argument from the one the researchers had.
First plants caused ice ages, new research reveals : https://www.sciencedaily.com/releases/2012/02/120201094923.h...
Like you mentioned, CO is bad for us because of our hemoglobin. Otherwise I could imagine life using an otherwise chemically interesting molecule like CO (it can oxide further).
CO2... not so interesting. Aside from the reaction to make CaCO (?) and acidic when dissolved in water it’s quite limited being fully oxidized.
You need the ability to make things out of your molecules. Stuff at the ground state are boring!
Plants expand energy (otherwise wasted sunlight) to convert CO2 into O2 to make an interesting molecules, namely starch with which they can do something. If they had an endless supply of starches, they wouldn’t have bothered evolving with photosynthesis - just like we don’t care for photosynthesis since we have plants.