It all looks like political fight between Plan A and Plan B. You suggest not to implement Plan B as it would show real need to implement Plan A (cutting emissions).

That's one thing. But also, let's say that we choose Plan B, and this is taken as a sign that reducing emissions is unnecessary and global emissions soar. We then start pumping aerosols into the atmosphere to cool the climate.

Then something happens and this process stops: we face unexpected technical hurdles, or maybe the implementation of this plan has been largely left to a smallish number of nations and they are incapable or unwilling to implement it anymore, perhaps a large-scale war occurs, or something like that. Because of the extra CO2, we'd probably be worse off than if we had even partially succeeded with Plan A. So what's the expected payoff of choosing A or B?

As I said, I'm a bit wary of this, but I also think that it's important to research climate engineering technologies and make plans so that they can be implemented if (and probably when) necessary. The best option would probably be a mixture of plans A and B, but as you said, it looks like a bit of a prisoner's dilemma.