CO2 is absolutely poisonous because it prevents you from getting oxygen.

CO2 is absolutely a pollutant. Nitrogen, which you've already identified helps plants, will also kill you.

My analogy to shit is to point out that something being "natural" doesn't make it not a pollutant. If you don't like "shit" we can go with: uranium (which is naturally occurring and definitely a pollutant), methane (which is also naturally occurring and defini9tely a pollutant), and volcanic ash (which is also naturally occurring and definitely a pollutant)