1) CO2 concentration has a long half-life in the atmosphere, so even if we immediately stopped emitting every molecule of fossil fuel-derived CO2 into it, we'd still see the effects of what we've done for the past century for at least another couple centuries.
2) People mostly hope to lower the rate at which our CO2 emissions rate increases, and maybe in certain countries make it negative. Both of those, however, are derivatives of the relevant value for purposes of the greenhouse effect and ocean acidification: the absolute level in the atmosphere. Which has zero chance of decrease even under the most aggressive conceivable prevention efforts.
3) The graph doesn't even cover the last major glaciation event: the last glacial maximum was around 20k years ago.
4) Biggest issue: the people who will be most adversely effected by climate change are people who don't have the resources to adapt. I don't dismiss the idea out of hand that it might be cheaper to put efforts into mitigation than prevention: we're definitely going to have to do some mitigation work. But you are not going to convince Western countries to spend trillions of dollars building levees in Bangladesh.