Keep in mind that there were no plants on land prior to 450 million years ago - their growth was largely responsible for the reductions in CO2 seen on your graph. But this is now, not millions of years ago, and we have to deal with and think about conditions we see now. The changes that happened during the time period of the chart were vast, sharply modifying the whole world, at least the living part of it.

Of course life as a whole survived, but most species did not. Do we want to be one of the casualties of the next mass extinction? And do we want it to occur at our own hands? I don't think anything we do one way or another will likely result in the kinds of major extinction events shown in the fossil records, but even a m inor one would be devastating to Homo sapiens, not to mention a lot of other species.