Ordinary everyday metabolic processes produce a certain number of free radicals--unstable molecules that can interfere with the functions of body cells in important ways. Some interference can be with cell reproduction, replacing healthy cells with daughter cells that have DNA damage from the free radicals. Free radicals can also interfere with cell functions, such as the manufacture of enzymes, etc.
Antioxidants join with free radicals in the body to render them harmless. There is only a limited supply of antioxidants, they are supplied mainly by diet. A number of foods, INCLUDING FRESH COFFEE, have a high level of antioxidant chemicals in them which help prevent degenerative changes caused by the free radicals.
Antioxidants are real, and they are a GOOD thing--help you stay physiologically young and healthy. Not hype. ;-D
(Simplified very basic explanation, hope it helps.)
The "story" behind antioxidants you relate quite clearly. I have no doubt of the chemistry you describe.
It strikes me that this simple chemical bonding mechanism is applicable to a wide variety of reactions, chemicals and nutrients. It is almost like saying "wet is good", referring to the body's need for water.
There are too many nutrients with antioxidant properties for that attribute to provide much guidance. The studies I've seen (though I have not seriously researched this) show that various good foods and nutrients which are among those with antioxidant properties have various healthy affects, but it is seldom clear that it is exactly the antioxidant property that is responsible for the healthy affect, and too often supplementation with the specific antioxidant chemical (vitamin, mineral, ...) is less successful in demonstrating healthy affects. While such clinical trials seem to be inconclusive, it is patently clear from the labeling and marketing of nutritional supplements that the word "antioxidant" has become a sales driver, rather like the word "sale" for women's clothing.
The end result is that I have not found the label of "antioxidant" a useful guide in selecting nutritional supplements.
My intuition is that specific remedies for specific ailments, such as tumeric for arthritis, aren't simply a case of "antioxidants are good", but rather have more specific affects, caused by specific compounds, on the particulars of the ailment.