[tasty_freeze]

> Don't plants require carbon dioxide to grow

Of course. Nobody is saying there should be no CO2. But if your implication is that higher CO2 means better growth, it is generally wrong. Some plants do grow better, some don't, in a higher CO2 environment. But more importantly, it isn't as if CO2 is an independent variable. Along with it comes significant changes that plants are not adapted to -- higher average and peak temperatures, more or less rainfall (depending where in the world it is). Yes, given enough time, the plants that make it through the stresses of climate change will adapt and thrive, but in the near term (a few generations of humans) it will cause problems.

> I am not sure it was immediately obvious to people 120 years ago that CO2 was such a "dangerous" thing.

https://en.wikipedia.org/wiki/Greenhouse_effect

In short: Joseph Fourier (of the Fourier transform) advocated for the idea of atmospheric gasses causing a greenhouse effect. It was advanced along the years, in 1896 Arrhenius even calculated the effect on the climate due to a doubling of CO2. There were scientific papers published in the 50s using the terms "climate change" in the 50s, well before the Mariner 2 spacecraft.