Oxygen is an amazingly energy rich fuel and is super abundant for us. The oxygenation of earth was one of the key steps, and it might be a "hard step" for other civilizations.

Of course oxidation causes a lot of damage and byproducts, and is one of the causes of our aging and death. But without it, well...

I was primarily referring to particulate matter suspended within the air we breathe. High PPM / particulate measurably reduces lifespan in several population studies, and it also produces noticeable pulmonary and cardiac disease states.

Polluted air is bad.