By trying to impose such restriction on the use of 'they' as a singular (what about 'you' short for "you all" as plural?), you are creating conflict of your own rather than letting life go on.
Those who see the world in terms of good and evil tend to do more evil themselves. Take care that your perception of militancy does not similarly take over your own effect on the world.
I don't impose anything on anyone. I don't restrict what anyone says. I don't really care all that much what other people want to say or do within at least some degree of reasonableness.
I simply choose not to put myself in a position where I must interact with those who want to tell me how I must use a language that predates their existence by thousands of years.
Those who see the world in terms of good and evil tend to do more evil themselves. Take care that your perception of militancy does not similarly take over your own effect on the world.
Peace.