The Washington Post is allowing singular they, and the sticklers have raised the drawbridge, lowered the portcullis, and barricaded themselves in the keep. Unfortunately for them, there is a wide world beyond the glacis where their influence is increasingly tenuous.
Before proceeding, I ask you to look at two things. In the first, a post, "Acknowledging the Inevitable," Bill Walsh of The Post explains the changes in the paper's stylebook. In the second, Tom Freeman, the Stroppy Editor, explains the issues associated with singular they in detail. He includes some salient information about the nature of English pronouns, the extensive historical use of singular they, and evidence that it is increasingly common in published work. (It has always been commonplace in speech.)
Now let's have a look at some of the objections, culled from comments at various articles and sites.
One of my first editors (almost 17 years ago) instilled in me this important grammatical rule. I still follow this rule.
This is a variant on the What I Was Taught response, usually echoing some high school English teacher. Unfortunately, a great deal of nonsense is taught in the schools. In many Southern states, the history textbooks suggest that slavery was a secondary or minor issue in the Civil War, when anyone who has troubled to look at the historical record understands that slavery was the political, economic, and cultural issue for the late Confederacy. And in those states in which fundamentalist Christians have taken over the school boards in a putsch, you will find creationist claptrap in the science texts. A great deal of what we learn in school must be laboriously unlearned and relearned in later life, and English usage is no exception.
A new word is needed, IMO. However, 'they' is already taken, and it is plural.
Just about everyone acknowledges that English is hampered by the lack of an epicene third-person singular pronoun. And many of them say, "Let's invent one." They are evidently unaware of Dennis Baron's list of the failed epicene pronoun proposals since 1850.
Attempts to engineer changes in the language are rarely successful. What happened with the English lack of a third-person-singular epicene pronoun is analogous to Stephen Jay Gould's account of the development of the panda's thumb. The giant panda uses a digit to strip leaves from bamboo, but it has no opposable thumb. Its "thumb" is a wrist bone enlarged and elongated over time as evolutionary selection adapted the part. Similarly, English found centuries ago that they could be readily adapted to singular uses and has happily used it so ever since.
I don't like it.
By far the most common negative response. We all have individual aesthetic preferences, but enshrining them as Rules of English goes a little beyond our writ as writers and editors. Those who dislike singular they, or are cabined, cribbed, and confined by a restrictive house style, can continue to convert singular into the plural, use the cumbersome and tedious his or her construction, employ s/he, alternate his and hers, or recast sentences altogether, in order to avoid a simple, clear construction that everyone understands. From my seat, it looks like a good deal of wasted effort.
I think it was probably a combination of What I was Taught and I Don't Like It that produced the kerfuffle in 1993 when the Chicago Manual of Style suggested in the 14th edition that there were contexts in which singular they would be acceptable. Chicago backed down* and now says that though it is common in informal usage, it is not acceptable in formal usage.
When argument and evidence fail, there is always name-calling to fall back on.
The next generation can mangle on. 'They' will always be plural as long as I'm at the keyboard.
This is the one I like best, suggesting that Anno Domini is well on the way to resolving the issue.