I do believe that something like what you're suggesting is going to be necessary to avert the total collapse of civilization as we know it. However, the part that trips many up, including myself, is that what you are proposing is a last ditch effort which should be taken after all other reasonable steps have been taken. I think we'll get to the point where that discussion is necessary, but first we need to do what we can to limit emissions. If we don't then we're just going to give those with the power and influence to make changes an excuse not to.

In short, we can't even get the world to agree to address the problem in a reasonable timeframe. That step has to be behind us before we start seriously considering geoengineering in pretty much any form.