It’s been in use as a singular pronoun since Shakespeare and no amount of denying that will change the facts. It simply is a fact. This is what non binary people have chosen to use the most often and if you aren’t in that category you don’t get to decide that a perfectly legitimate use of the word shouldn’t be used.

Your problem with the English language isn’t anybody else’s fault. Do you think you know better than Shakespeare? If you do then sure, use your graduate education in English to change the rules.

People use singular they all the time. It’s linguistically correct to do so. “Who left their ticket on that seat?” That’s singular and you know it. “I think they went to the bathroom and they will be back soon.”

It really isn’t a problem except for people who want to make it a problem so they don’t have to do anything they don’t like.

Using facts isn’t gaslighting.