The topic of the article discussed is an approach reducing the CO2 in the atmosphere, to fight the current and ongoing climate change. This sets the context for the discussion. Yes, in geological times, we had much higher CO2-content and some of the plants are still rather optimized for that. This is interesting information, but is an entirely different topic - though it is an argument often used to deny the harmful impact of CO2 onto the climate.

Also, the sole concern of the human species is the survival of the species. Of course we should try to ensure this survival in the most ethical way. Protecting the environment comes from those concerns. Climate change is a very big danger to our civilisation right now.