The Danger of Unverified Prescriptivist Complaints:

A commenter provides the following:

Back to the subject at hand: One of my own pet peeves is the use of "insure" where the writer clearly means "ensure". "Affect" for "effect" is just as bad, but not nearly as common; these days, it seems like everybody and his dog misuses "insure". I'd check a dictionary or style manual for support, but I'm worried that the new usage of "insure" has become so common that they may consider it correct.

Oh, buddy, it's worse than you can imagine. Much worse. From the Oxford English Dictionary definition of "insure" (definition 5 is the modern one, but I include #1 because of the back-reference to it in #5):

1. trans. To make (a person) sure (of a thing); to give security to (a person) for the fulfilment of something: cf. ASSURE v. 9, ENSURE v. 1, 2. Obs.

c1440 Promp. Parv. 262/2 Insuryn, or make suere, assecuro. 1681-6 J. SCOTT Chr. Life (1747) III. 21 Thus Christ..hath taken the most effectual Care to insure the mutual Performance of this everlasting Covenant to both insure God of our performing our Part..and to insure us of God's performing his Part....

5. trans. To make certain, to secure, to guarantee (some thing, event, etc.): = ASSURE v. 5, 7a, ENSURE v. 8, 9.

1681-6 [see sense 1]. 1809 W. IRVING Knickerb. VII. xiii. (1849) 450 Such supineness insures the very evil from which it shrinks. 1821 MRS. SHERWOOD Hist. Geo. Desmond 19 He had insured for me the situation of a writer on the Bengal establishment. 1849 RUSKIN Sev. Lamps vi. ยง8. 170 Want of care in the points which insure the building's endurance. a1862 BUCKLE Civiliz. viii. (1873) 462 An ardour which could hardly fail to insure success.

It's not that the new usage of "insure" has made it "become" correct. It's that "insure" to mean "ensure" has been standard English since the late 1600s. "Insure" to mean "secure the payment of a sum of money in the event of loss of or damage to property" is attested in the OED only fifty years earlier (1635), and even that quote uses "ensure" and "insure" interchangeably: "Authorising your petitioner to ensure all your majesty's subjects whatsoever for soe much of their estates combustible as they themselves shall conceive in danger of Fire, not taking above 12d. per centum yearly for soe much soe insured."

Now as it happens I don't like "insure" to mean "ensure," either. Using "insure" may lead the reader to think of insurance, which may thus be slightly distracting. Such usage would almost never be ambiguous, because the following word or words will make clear which sense of "insure" is meant. And English is so full of words with multiple meanings that English speakers are unlikely to be much distracted by another such word. Still, I have an esthetic preference for limiting "insure" to situations involving insurance, and perhaps there's some practical benefit for following such a practice.

But it's one thing to say "potentially needlessly distracting," "esthetically displeasing," "inelegant," or "pet peeve[]" -- it's another to say "misuse[]" or "[not] correct." When current dictionaries report that this usage is common today (see, for instance, this Usage Note, this definition, and this definition), and when the usage has been attested in the Oxford English Dictionary since the late 1600s, how could even a prescriptivist credibly argue that it's wrong?