And the ozone treaty was not signed until governments were certain that cost effective alternatives existed and could be deployed at the scale required. With CO2, we can only nibble at the margins of the problem because there are no cost effective and politically acceptable alternatives that can supply all or even a significant portion of our energy needs.
Every country in the UN signed onto the Montreal Protocol because they all realized the damage the hole in the ozone was going to do to the environment, not because it was going to be "cost effective". I guess if we all had your attitude to ignore such issues simply based on cost, we would all be severely sun burnt by now.
No thanks.