I'm in the tomb world, marking essays.
Some are quite good, others we shall simply pass over in silence.
As a group, however, they make me feel even more bitter towards the anti-humanities-education slags at The Australian than usual. As I've noted here recently, one of the unfounded slanders emanating from those people is that unionised and left-voting teachers don't care about spelling and grammar. In our mad Stalinist scramble to instil political correctness into innocent minds, it seems, we encourage students to seditiously mangle the Queen's English (Queen Victoria's) and to express themselves through creative spellings.
This is a very hurtful accusation. I care more about spelling and grammar mistakes than about almost any of the other kinds of lapses students make. Also, I would happily spend our pitifully limited class time on teaching my students how not to go on making the same mistakes they made last time, if it was allowed, but because students must be taught what the university handbook says they'll be taught, it is not allowed.
My particular bugbear today is born of a mixture of vague PC intentions with a limited grasp of basic grammar. The post title is one example. Here are some more:
Mr Xyz has no awareness of what is owing from a man to their offspring, and they consequently suffer from his mistakes well into their adulthood.
A young lady in that society was expected to find a husband for they had no other way of providing for themselves.
If a naval officer captured an enemy ship, they were given prize money from the King.
In each of those sentences the subject is a member of a class whose gender is already a given and so it's natural and correct to use a gender-specific pronoun, but the writer thinks it's a good idea to use "singular they" in place of any gendered pronoun which doesn't apply directly and immediately to a single personalised individual. The writer thinks the gender neutrality imperative always trumps any other rule which might be governing the formation of a sentence. It doesn't. Gender neutrality is a positive nuisance in a sentence where gender is already established.
The range of formal writing situations where "singular they" is the best option is very small. A good half of all cases can be resolved by rewriting the sentence to pluralise the subject, or, even better, to individualise the subject. Writing that randomly patters on about what "the reader" might deduce from a page of prose if "they" are awake and reading, is just not as interesting or convincing to read as writing which isn't afraid to own some of those deductions, or to at least attribute them to a plausible person. If I'm writing about readerly responses which are in fact largely my own, I use the feminine, since I'm a lady. If I'm writing about the general cast of critical opinion in a time & place when expressing such opinion was largely the prerogative of men, I'll use masculine pronouns. At other times, I find "he or she" or even "s/he" works well enough. It may be a bit ugly-loooking but at least it's precise.
None of this is to say that I abhor and eschew the use of singular they. I only dislike seeing it used as the default. If you're an artist with language and you know what you're doing, you can use whatever pronouns you jolly well like, and I'll look on admiringly while you do it.
(On the other hand, the snaggy deployment of "she" instead of "he" as the universal pronoun can and does backfire quite badly especially when it's done in a piece of writing that's hostile to the stance which the he or the she is being made to adopt. The [unintended?] effect is of condescension.)
My hunch is that people over-apply this 'rule' because it is has a clear and accessible rationale - don't be sexist - and because it's one of the few positive rules to do with grammar they've ever been given. If more people understood what subject-verb agreement was, or indeed knew that sentences require both subjects and verbs, there would be much less of this sort of writerly imprecision, and my head would not have so many bumps nor my desk so many gashes.