Read on maritime SO2, it was stopped because it's second order effects were too negative (mostly acid rain if i recall right)
The stuff about aerosols: The "plan" isn't that you dump a one time "treatment" of aerosols and then climate is reset. It's a continuous aerosol injection advitam aeternam to offset the warming - constant upkeep.
About comments on destruction of all life: the biosphere is so conplex it's hard to even grasp the gist of it. Global temp affects every level of it. Were this "treatment" be a little too strong/maladjusted, it could very well cause runaway mass death.
And we only have proof of life on earth - if we kill life on it, as far as we know, it's over for life itself. Can't be careful enough, and aerosol dispersal isn't that.