1. Corruption cannot include legal behavior in which every ("reasonable") human partakes. [Implied: because it is legal]
Therefore, 2. Ethical standards are encoded in law.
Therefore, 3. Ethical behavior is governed by law.
Therefore, 4. Voluntary actions not specifically compelled or disallowed by law have no ethics.
My point is that it is possible for something to be legal, common, sensible from a perspective of pure self-interest, and still wrong and worthy of reproach.