What could possibly go wrong is basically this — small changes in the radiation budget (incoming solar energy) might be fairly minor in their effects in the tropical and temperate climate zones, let’s say they manage to reduce the incoming solar radiation by 1%, that would leave our climate colder by perhaps 1-2 C deg, but the big unknown is the effect in higher latitudes which are much more sensitive to rapid changes in climate in relatively small changes of energy budget. That is the main reason I would fear this proposal, and there’s no control planet to test this out before applying it here on earth. You could easily tip the balance rapidly towards the onset of a major glacial advance or an “ice age” climate and once you set that into motion, just stopping the aerosol program will not guarantee a reversal of those effects.
Fortunately I think this fact is well understood by those in the profession and if these proposals go much further they will probably start speaking out against the idea.