Ok lets play this game. The fact is that H20 is not a pollutant. It's a molecule that sustains life and a key component of the biosphere's life cycle.
Bring on the ice age!!
The problem: If it's a good thing... whatever. If it's a bad thing... Mass Death. Seriously, that's not an exaggeration. Any slight imbalance and we're talking catastrophe. Unless you don't think natural disasters matter much.
We're not saving the environment we're saving our goddamn selves. The environment isn't even a thing. But humans are, and we need a stable environment to get on with our lives.
In order to take the "Mass Death" scenario seriously I want to see some credible indication that our environment actually is that fragile. What I do know (and again, I'm not a specialist) is that most catastrophes that actually happened in the distant past would be expensive for our civilization, but not "catastrophic". Worst case scenario would be something like making a 20 degree belt around the equator a desert, while at the same time making Norther Europe/Asia/America greener (or the other way around). Bad? Depends who you ask. Definitely catastrophic for the equator countries, but not for the humanity as a whole.
Thus, there's no point in controlling it, or making sure it doesn't accumulate.
(The next time a person in Congress tries the "CO2 is natural etc" gambit, I'd love someone to stand up and ask if that person has stopped wiping their ass.)
Maybe people are not aware that most things are toxic in concentrations higher than natural, including, for example, oxygen. And even if elevated CO2 caused humans to walk around in a blissful high, it would have nothing to do with its impact on climate...
An interesting game to play with the H20 "non pollutant" is to see how much of it you can consume before you become ill.