"You simply aren't going to have modern society without billions of people."
I don't see why not quite honestly, a few hundred million could easily be enough.
" You can have 2 people and still produce too much CO2 for the earth to handle "
Now you're being silly.
"And you simply aren't going to revert 7 billion people back to an agrarian economy. "
So what, I've never heard anyone suggest we should do this.
Less people = less waste. The problem is one of polluting less and recycling more, and reducing the human footprint upon the ecosystem. Clean energy is not a problem, we've solved that 10 times over.