I've generally come to the belief that it's related to how humans think about cause and effect.
Dumping boatloads of CO2 into the atmosphere is second order from the actual goal of producing electricity so most people just can't/don't/won't think about it.
In this case we'd be intentionally dumping SO2 so people are capable of thinking "wow that's not moral" or whatever issue they might have with it.
I think the biggest concern with something like releasing SO2 as a geoengineering project, which needs, quoting someone else in the thread "very little" to be released to have a big effect, the concern is over-correction or unforeseen effects caused by an insufficient understanding of the system as a whole.
Don't want to accidentally start an ice age by trying to prevent a hothouse planet from forming :P
And we want to stop releasing CO2. We don't want to wind up charging onwards to 1,000 ppm CO2 just because we released enough SO2 to compensate for the climate change.
Eh, don't worry, the rich among us will bottle up the 'good' air and, well, just watch the clip from the documentary "Spaceballs" - https://www.youtube.com/watch?v=Lz0xULQIaSU
Dumping boatloads of CO2 into the atmosphere is second order from the actual goal of producing electricity so most people just can't/don't/won't think about it.
In this case we'd be intentionally dumping SO2 so people are capable of thinking "wow that's not moral" or whatever issue they might have with it.