Fun stuff!
It's a case of a cure that could be worse than disease. It's a case of desperation compelling a solution with unforeseen consequences.
What I find interesting is that anyone could do it. Large scale conversion to renewable energy, reduction of meat production, slowing deforestation, these take nation-scale or global scale organization, enforcement. But any country, any multi-millionaire could dive into geoengineering. If Elon Musk starts putting chaff dispensers in his rockets could anyone do anything about it? You could ban it in one country, but then he just launches somewhere else. You think someone with a hundred million dollars can't convince some tiny government somewhere to let him use their runways to fly his glitter dumping airplanes?
So while we all have to debate and participate (voluntarily or otherwise) in other mitigation, this is a solution that could be implemented with 90% of humanity not only non-participatory, but disapproving.
Imagine an oil-producing nation that's a bad actor (tough to imagine, but let's pretend). Wide scale adoption of renewable energy pushes the price of oil down, so they sink some of their billions into any one of a half-dozen plausible geo-engineering projects (the book Superfreakanomics described several). Now they can advertise: "fossil fuels are safe again!" and "your petro dollars help pay to cool the Earth!"
Reducing carbon output hasn't been too painful so far, but to get levels down enough to matter it's going to be hard. Geoengineering is easy. Human nature makes it seems inevitable. Not necessarily good, but inevitable.