IMO the problem here is the leap of faith you are making by believing an untested technology, operating on a planet scale, will help.

We only have one planet here, so instead of betting on a massive terraforming technology to suck the CO2 out of the air, I'd rather use a more conservative approach such as massive reforestation - something that is low-tech, can be done by anyone, anywhere, and improve the resilience of the ecosystem rather than kicking its balance again.