Those 150 years of direct climate measurements didn't show much warming until they were "adjusted", but that's really beside the point.
The point of the debate is: what human action will make the life of humans better. Do we know enough to do a cost-benefit analysis on various plans? No. Do we know enough to know whether the climate will become warmer or cooler (not the bias introduced by humans, which is clear, but the total system behavior)? No, we don't.
Yes, yes, everyone understands what CO2 does, that's really not the issue. The complex system of feedback loops, many positive and many negative, that is our climate isn't well understood, and isn't yet successfully modeled. The atmosphere itself is a chaotic system, but no one would model just the atmosphere - the oceans are a far more powerful driver for climate, even for CO2 levels.
But, really, the single largest factor in determining "warmer or cooler" isn't human activity, or the atmosphere, or the oceans. It has driven quite dramatic climate shifts throughout the Earth's history, likely including extinction events, and including a 100k year cycle that we're at the peak of, and it's not well modeled and only modestly understood.
So, no, no one's debating how CO2 works. But that's a small part of the story, and not enough to inform policy.