Excess oxygen is actually harmful to humans, but all the climate warnings are about losing oxygen, not nitrogen edit: but when we look for habitable planets, our focus is ‘oxygen rich atmosphere’, not ‘nitrogen rich’, and in medical settings, we’re always concerned about low oxygen, not nitrogen.
Deep sea divers also use a nitrogen mix (nitrox) to stay alive and help prevent the bends, so nitrogen seems pretty important.
It seems weird that our main focus is oxygen when our main air intake is nitrogen. What am I missing?
edit: my climate example was poor and I think misleading. Added a better example instead.
Nitrogen is usually in the form of N2 and is very stable. We don’t really do much with this form of nitrogen because chemistry is hard so with each breath it just hangs around. The oxygen on the other hand js readily absorbed and used, converting it into CO2. We have to remove the CO2 to prevent toxicity and add O2 to prevent suffocation.