Here is a thing dumb people say about carbon dioxide pollution:

lol carbon dioxide isn’t bad for you I totally exhale it and stuff. Also, plants need it to eat I read somewhere, and I hypocritically rely on that bit of science as a counterpoint to your asking that I stop burning tires in my toilet

Here is something you can say in response to such people, if you want to keep talking to them, which you should not: Too much carbon dioxide is bad for plants, too.

From the Max Planck Institute:

[T]he more carbon dioxide the better? The equation is unfortunately not as simple as that. The plants, which ensure our basic food supply today, have not been bred for vertical growth but for short stalks and high grain yields. Scientists from the Max Planck Institute of Molecular Plant Physiology and the University of Potsdam have now discovered that an increase in carbon dioxide levels could cancel out the beneficial effects of dwarf varieties.

IR8
IRRI

The story, in short: A variety of rice known as IR8 (pictured above) was bred to have a shorter stalk, allowing it to use its nutrients to produce more rice, and then to better bear that rice’s weight. According to the institute, “Plants like IR8 succeeded in protecting humanity against global famine and were hailed as part of the ‘Green Revolution’ in agriculture.” Unfortunately, increased CO2 levels have blunted the strain’s positive effects:

Although nothing has changed in the genetic makeup of the IR8 rice plant in the past 50 years, its yields have declined continuously. The researchers working with Bernd Müller-Röber from the Max Planck Institute of Molecular Plant Physiology and the University of Potsdam therefore wanted to find out whether this development was possibly linked with the global increase in atmospheric carbon dioxide levels. After all, the current concentration of the greenhouse gas in the atmosphere is 25 percent higher than in the 1960s.

… [R]esearchers were able to observe that a higher carbon dioxide concentration results in the unblocking of the capacity of dwarf plant to form gibberellic acid. The carbon dioxide appears to have the same growth-stimulating effect as that triggered by the gibberellic acid. Thus, in the experiment, the dwarf plants gradually lost their advantage and increasingly resembled the control plants.

So, yes, plants need carbon dioxide. But the lesson we should learn from this experiment is the one we should have learned about the atmosphere: You can have far, far too much of a good thing.

But by the time you explain all of this, the dumb person to whom you were explaining it has probably gone off somewhere to win a Darwin Award. All this preparation, for naught.