Eh.... . Too over abundant of any chemical are bad including oxygen (You can drown or unable to breath if too much oxygen) you know, thats why the planet ozone are being affected because the CO2 are over the planet threshold, if you are talking about carboniferous period theres a reason mass extinction happen there with how volatile and easy to forest fire occur there, because the plant produce oxygen so much and deplete the CO2 starting the ice age period, not including we got giant insect.
What we need are balance of the planet element.
The man made "Pollution" are what geo engineering anyway even though its probably not intentional effect, thats why we get this global warming in the first place, because like it or not CO2 effect increase planet temperature.
And either this method or we embrace human extermination or extinction, eitherway is fine to me to be honest.