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.

The short version is that life needs something that's at least a little unstable in order to extract chemical energy from things.

The post is correct when viewed in a particular light, on a technicality, if you squint. By that same technicality iron rusting is also burning very slowly. They're ignoring the rapidity which is implied by "burning". But yes, oxygen is unstable, oxygen helps burn things, and oxygen is toxic if you get too much at once. Though you'd need to be breathing pure oxygen pressurized to about 1.4 atmospheres, or regular air pressurized to about 7 atmospheres, for that last one to happen. It's a legitimate concern for deep SCUBA divers.

But why does life need instability? Chemical instability is, in basic terms, just stored chemical energy, and that energy wants to be released. The more reactive something is the easier it is to get energy from reactions involving it. There's a balancing act here where more reactive means easier energy, but also more dangerous. Oxygen is in a kind of sweet spot where it's stable enough that it's not generally going to explode or catch fire on its own, but can be coaxed into doing those things in controlled ways with other chemicals to extract energy when needed.

There are anaerobic bacteria that don't need oxygen to survive. That was the norm before The Great Oxidation Event when cyanobacteria started releasing oxygen into the atmosphere during photosynthesis. Prior to that there was very little oxygen in the atmosphere, and anaerobic bacteria ruled the world.

After the GOE the high concentration of oxygen killed off most of the anaerobic bacteria, and what was left were organisms that made a blood truce with oxygen. Aerobic organisms gained incredible power from utilizing oxygen for metabolism, but eventually die from the accumulated damage the oxygen does to them.

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

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

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

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

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.

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

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