I suppose the first thing to ask is "What can go wrong?"
Answer: Not much. Volcanoes already do this, so it is not something unprecedented. If we change our mind, we can stop spraying the aerosols, and everything will return to normal in a few months.
Our planet maintains a balance so far
Well, the whole point of AGW is that we are already out of balance.
I don't really like the aerosol idea. It doesn't actually remove any CO2, so things like ocean acidification will continue to get worse. If we are going to do geo-engineering, then iron fertilization of the oceans seems like a much better idea. That removes the CO2, and boosts fishing yields. But we should be doing lots of research on ALL feasible solutions.