Setting aside the impression I get that the original problem was worded so as to exclude possible mechanisms, and to force defense of only one of several alternate explanations (or suite of explanations), the overall approach is reasonable -- when faced with two options, choose the one that minimizes possible loss. But the unspoken assumption is that a) we are faced with only two options,
b) we know how to reliably price cost versus loss values,
c) we can develop a control strategy (modulate temperature by modulating atmospheric CO2 while keeping planetary albedo constant) that has a decades-long feedback loop -- i.e., to determine if the method is working with enough certainty to redouble it as needed, or alternatively to reverse it, would take an entire human lifetime.

I am particularly skeptical of people who pose a problem in such a way to force a 'solution' that they had already desired BEFORE the problem even appeared. Examples of such suspicion-raising 'solutions' include massive planetary de-industrialization ('greening'), massive increase in regulationist reign over commerce and transportation down to the family and individual level, and the old standby, "elect Al Gore and the world will be saved." I know a lot of intelligent people who sincerely advocate actions such as these (which may even be defendable), and they have been working on developing different justifications for them for many many years.

Motivations for academic enthusiasm for fad science should not be that mysterious. Fads are what drives funding (e.g., Hansen's grants from the Heinz Foundation), and save-the-world campaigns are eminently ego-gratifying and news-media-attention-grabbing.

Furthermore, being out of step with the fad gets you accused of intellectual whoredom on national television, gets you likened to pro-Nazi 'holocaust-deniers', it even is getting some people sued by environmental groups, and now there's a call for 'world crimes trials' for speech in opposition to the fad. Who needs that? Only people not confident in their own arguments.

These don't make the fads non-scientific a priori, but they should caution us that just because some say that "scientists agree" to something (even especially when it's not entirely clear that the relevant scientists actually DO agree) doesn't mean that they, as human as the rest of us, reached those conclusions from totally dispassionate logic.

Add to it the current world intelligentsia fad to blame everything from hair loss, drowning polar bears, blind Patagonian sheep, all the way to lower sperm counts, on US national greed and stupidity, and there's a prescription for stepping back, taking a few deep breaths, and seeing how much of these themes are over-hyped. And for trying to avoid inflaming the hype.