'non-citizen' sounds pretty negative to me. Sounds worse than foreigner in a way to my ears.

Thanks for all the thoughts everyone... this is interesting.

Cecilia,

As someone mentioned earlier, using 'their' with singular nouns has been a part of English for hundreds of years. It may not sound as formal as some other options, but at this point it's definitely part of the language.

Of course it's a result of English not having a neuter singular third-person pronoun. Saying 'his or her' instead of 'their' is cumbersome and formal sounding, at least to me.

For example: 'Everyone did his or homework.' That doesn't sound very good to me. I see nothing wrong with using 'their' in that situation.