Descriptivism, prescriptivism, and assertionism—here, as to 'entitled' used to mean 'called'
As I've noted before, while I have philosophical disagreements with prescriptivists about English usage, my main practical disagreements are with people who might be labeled "assertionists." These are people who don't just say that prescriptions set forth by some supposed authorities define what is "right" in English—instead, they simply assert a prescription even in the face of what those supposed authorities say. Usage X is wrong, they say. Why? Because it violates this rule. What's your authority for the proposition that this is a rule? Well, it violates the rule.
I was reminded of this by the latest mini-eruption of the "you can't use 'entitled' to mean 'called'" argument, noted by Prof. Mark Liberman (Language Log). Ross Douthat (New York Times) disapproved of a review of Marco Rubio's new book and tweeted that the review "could have been entitled: 'I Think Rubio's Book Isn't Good Because I'm a Liberal.'"
This led to several tweets in response, condemning Douthat for using "entitled" this way; I've seen this claim—that "entitled" can't mean "called," when applied to books, articles, and the like—before in other sources, and have even blogged about it. And it's a classic example of an assertionist claim: something is condemned as wrong based merely on the speaker's say-so, without any real prescriptivist evidence.
After all, if you look in dictionaries (e.g., the Random House, the American Heritage, the Merriam-Webster, and the Oxford English Dictionary), you'll see one definition of "entitle" as being some variant of "To give to (a book, etc.) a designation by which it is to be cited, or which indicates the nature of its contents" (I quote the OED here). There is no hint in the dictionaries that there's anything wrong with this.
Ah, you say, but those are Evil Modern Descriptivist Dictionaries. Very well, let's look in the Good Old-Fashioned Dictionaries, such as the 1913 Webster's and 1828 Webster's; we will see the same thing. Indeed, if we look in the OED, we see the use attested back to Geoffrey Chaucer. Likewise, if we look at the work of a prominent modern prescriptivist—Bryan Garner—we see him approving of the "a book entitled …" locution.
Now there is one significant source that does condemn "entitled": The AP Stylebook says, "Use it to mean a right to do or have something. Do not use it to mean titled. Right: She was entitled to the promotion. Right: The book was titled 'Gone with the Wind.'"
But much of what such stylebooks contain is advice about style—about what the authors see as more elegant or clearer—and not an authoritative judgment about what is right usage and wrong usage in general. And, as Prof. Liberman's post makes clear, many publications do not follow AP style on this. Indeed, "book entitled" used to be vastly more common than "book titled" in published books, though now it is merely twice as common. Perhaps the great bulk of publishers' editorial departments were ignoramuses, and only the Associated Press has the one authoritative answer; but it's likelier, I think, that this is a matter of preference, and the AP Stylebook authors are expressing their preference.
If you prefer to use "titled" instead of "entitled," go ahead. (That's my preference, too, though I'd probably usually say "called.") If you think it's better, all else equal, not to use terms that have an obvious alternate meaning—and a meaning that is at least at times negative—that's a good argument. ("Fulsome" meaning "thorough" or "abundant" has long been standard English, but I don't recommend using it in that sense.)
If you are a publisher trying to set forth a uniform rule for all your employees, you're entitled to do that. If you think that "entitled" to mean "called" sounds a bit fussy and pretentious, that's a fine argument. And if you just want to assert that you like "titled" better than "entitled," be my guest. Aesthetic preferences are one area where assertion is just fine.
But claiming that someone has actually committed a usage error by using "entitled" to mean "having the title" should be based on something more than just assertion—whether you're a descriptivist or a prescriptivist.