While a huge amount of research needs to be done before this type of operation would be even considered for practical use, the idea itself is grounded in reason and has no real foreseeable downsides; at least by comparison to the downsides of global warming. Before a concrete opinion can be made, there needs to be absolute assurance that the benefits outweigh the downsides, but as of now, this seems like the best solution.
Solar shading by sulfate dust is a bad idea because there is no way to test the long range impact. It is a radical approach that the final result could easily be much worse than the problem we are trying to deal with in the first place. We often claim innocence because we were not aware of how destructive our actions were in the past. Now that we know how foolish it is to blunder ahead trying to force the earth to accommodate us we should change our actions accordingly.