I hope I shall live long enough to see manners make a comeback in American society. I agree with you that politeness should be recognized as nothing more than common decency, but it seems lately to be treated as a quaint anachronism in many spheres of social commerce.
One point I would add to your admirable essay. A gentleman does not reserve his gentle ways for strangers or for public spaces. In fact, he makes redoubled effort to show kindness, consideration, and respect — and yes, courtesy! — toward those with whom he lives and works.