“Geoengineering” is code for “all land belongs to the big-government/big-corporate criminal complex.”
It's worse than that. Unlike the AGW models, which don't match reality, the matheatics and physics behind the geoengineering models is almost certainly accurate. By dumping controlled amounts of various chemicals where they have the highest multiplier, we can almost certainly nudge global temperatures in the direction desired. The problem is that if we geoengineer and the "warming" we are counteracting does not compensate for our actions, then we get an ice age. Unlike a repeat of the Medieval Climate Optimum, an ice age would be catastrophic.