So... we agree on this? You are making the exact same point concerning the answer to the actual question.

Just one difference. You say poison should damage you in some way you say. I think that resulting in death is rather damaging don't you? And extra oxygen (But not dangerous amounts obviously) is exactly how you speed up removal of CO from a person.

Here's the thing. Damage is about overdoing. Insulin for instance. We agree this is necessary for a body to function right? Dump a large enough dose in a body and your body will shut down and you die. Sugar (by many called a modern toxin itself) is the anti-toxin in this case. It's not fighting the toxin but the effect until the balance is restored.

The way insulin works, the way O² works, the way N, CO etc. work is fine....until it isn't. At that point it becomes a poison.