I love it when a phrase that drives language prescriptionists crazy turns out to be older than their great-great-great-grandmas.
The oldest use of this one that William Safire could find, in a much-quoted 2006 column, was by J.E. Lawrence in the Nebraska State Journal in 1949 on frontier life: “It is what it is, without apology.”
But contributors on the board at the Straight Dope found it farther and farther back in time:
1873 (The Cornhill Magazine) “A paper is bought and read because it is what it is, and every contributor has a share in making it what it is.”
1836 (An Essay Concerning Human Understanding by John Locke) “First, Essence may be taken of any thing, whereby it is what it is.”
1726 (Joseph Butler, 15 Sermons) “Everything is what it is, and not another thing.”
Established precedent may not make you like it, but it removes the blame from kids these days, who have enough inherited garbage to deal with.