https://en.m.wikipedia.org/wiki/Oxidative_stress#Diseases

Antioxidants may help with some of those conditions, but others are based on such underlying dysfunction that it would be like trying to bailing out a boat with big hole in the side. They're just not gonna do anything for you.

A bit Overblown, but not really bs, from what I researched a bit ago

The dietary antioxidant fad is mostly BS. They're supposedly meant to counteract oxidative stress and specifically free radicals. Both of those things are part of a healthy life and you would die without them. So any real impact is not so simple as "just counteract those bad things". Dietary antioxidants don't always lead to higher intracellular antioxidant levels, either.

Some dietary antioxidants so lead to higher intracellular levels and may help buffer oxidative stress (like from exercise) but there isn't much evidence that it doesn't just boil down to "eating your vegetables is good for you".

Because we evolved on the Death Planet, and life, uh, finds a way

https://en.m.wikipedia.org/wiki/Adenosine_triphosphate

talking out my ass, I'm guessing its because oxygen is an energetic and highly reactive element, and therefore it can do lots of things and it does them really well (or at least strongly), or in general was just the best most direct means to accomplish the energy intensive tasks that were required given the biosphere we evolved in? I'm not sure how common/ vital oxygen consumption was before that one mass extinction where algae became overabundant and oxygenated the atmosphere and caused a mass extinction, it could have been a result of adaptation to that new condition- though I doubt this is the case

When we and other known organisms take energy from food we are actually taking molecules with higher-energy electrons, converting them into the high-energy molecules our cellular processes can use to do make cell things happen, and producing very similar molecules with lower-energy electrons. Rather than infinitely accumulating these molecules, our cells dump low-energy electrons onto another molecule that is amenable and thereby convert into a molecule ready to accept high-energy molecules from food (with a bunch of steps in between).

For us, as aerobes, the electron acceptor at the end of respiration is oxygen.

Oxygen as an electron receptor is newer than several others. Anaerobes came first. It was only after photosynthesis had produced a ton of atmospheric oxygen that it became a viable option, really. But it O2 is a comparatively good electron acceptor because the process in which it accepts those electrons allows cells to grab quite a bit of energy from that last step. It is fairly "electron needy" compared to earlier electron acceptors.

So, basically, aerobes get more energy per food unit (sugar molecule) than the vast majority of other creatures. You need it to live because it is an essential part of how your cells get food, namely, how it can recycle molecules at the last step of the respiration cycle.

Because our atmosphere is full of oxygen and nitrogen. Oxygen happened to be the chosen option for some reason, probably because nitrogen might not be reactive enough, idk I'm not a biologist or a chemist forget what i said

In physics being finite is actually a good thing, there is a quantifiable answer to living and to dying as part of our identity.

Same reason an alcoholic needs alcohol to keep from shaking, you're addicted. Go ahead, try to stop. You'll shake just like they do.

Organisms need some oxidizing agent to respire. We use oxygen because it's very highly reactive and thanks to photosynthesis is goddamn everywhere.