This is dead on; if I’d thought of it, I would have written it myself. ;) One thing you’re missing, though, is an example of where it is okay to be blunter—with very close friends, with whom you already have an understanding of a certain amount of respect. This doesn’t obviate the need for politeness, of course, but it does lower the threshold of importance at which it’s okay to be blunt. If I’m in a hurry in a shop, I’ll still be polite to the clerk, because they don’t know me well enough to know that I’m impatient and stressed, rather than just a jerk. I worry about this less when talking to a close friend who already knows I’m not a jerk.
I’m actually not a very good example of this, because my default setting for the courtesy slider is fairly high. I can do this because it comes naturally to me, so it takes very little effort for me to reap the benefits of showing respect to the people around me. It took me a LONG time to realize that this is not true for everyone, i.e. that it is very difficult for some people to understand, remember, or apply these social rules, and therefore only do so in select situations.
ETA: … and this of course doesn’t make me better or smarter or more useful than people who have trouble with it. I’m incredibly frustrated with how slowly I think in arguments or debates, and my inability to remember details which help in them. The people I know who aren’t good at showing respect in casual conversation tend to be good at these things. Another tradeoff, probably, although I’m not sure why it would be the case. (I know at least one person who’s good at both, but I think he’s made a conscious effort to be so.)
Upvoted on spec; I tabbed out the essay to read later. (Commenting mostly as a reminder to myself.)
ETA: Okay, yes, upvote stands, that was good.