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.