Singular “they” isn’t wrong if the subject is indefinite in either gender or number. However, it’s absolutely wrong when used as a definite personal pronoun, a

Singular “they” isn’t wrong if the subject is indefinite in either gender or number. However, it’s absolutely wrong when used as a definite personal pronoun, as it introduces new, irresolvable ambiguity where none existed before; e.g. I just heard Tom and Harry are getting a new puppy; I just ran into them while they were walking their dog. If you do not allow for singular definitive “they”, the meaning is clear. If you do allow for singular definitive “they”, whose dog is it, and who did you run into — Tom, Harry, or both Tom and Harry? The problem with “personal pronouns” is that they aren’t personal in the first place — pronouns exist exist solely for the benefit of the speaker and the listener, not the subject. They allow for two people in a conversation to refer back to an antecedent succinctly and unambiguously. That’s all. If they can’t do that anymore, they’re just extra noise.