Why is oxidation bad?
Well, let's look at it from the point of view of a structural engineer.
You erect a large structure, and invariably it will be an iron and steel structure. From the moment the metal is cast, you fight a losing battle against oxidation.
Moreover, the bulk of the structure will remain intact. It is only in the load bearing surfaces, where unions between different surfaces (and different metals!), the screws, the bolts, the joints, where oxidation will be most prevalent, and most active (and precisely in the places that bear a load). The structure is doomed to fail. It might be 50 years, or a 1000 years, but corrosion is thermodynamically downhill.
We have all seen pictures of monumental bridges around the world: the Golden Gate Bridge; the Sydney Harbour Bridge; the Hell's Gate Bridge. All are steel structures, and to this day each would have dedicated teams of corrosion engineers inspecting the extent of corrosion, and trying to fend off the inevitable.
Now, I have used the example of bridges, which, in a salt water environment, are especially vulnerable to corrosion. Similar precautions and inspections would pertain to office blocks, which are based on a steel frame.