I can see why a proliferation of different potentially gender-identifying pronouns beyond he, she, or (neuter) it could cause confusion. There has to be some level of common acceptance, some level of standardisation, and some level of numeric limitation to the gender-identifying pronouns used in legal documents.
If every pronoun on Tumblr, for example, were to be recognised as legitimate and therefore permissible to list on a legal document then there would be no real point in asking for gender at all (even when it's pertinent, such as is the case with medical records or access to women's shelters).
That said, I cannot see any compelling reason why a gender neutral pronoun is so terrible on work documents or even drivers' licenses. The fact of someone's maleness or femaleness is virtually useless without additional personal information such as date-of-birth, hair and eye colour, height, weight, ethnicity and other information concerning appearance.
Overemphasis on gendered pronouns is as rediculous to me as the complete lack of emphasis (wherein anyone can not only choose but actually make up pronoun in reference to themselves).
Seriously...
911 OPERATOR: Hello. Do you require police, fire, or ambulance?
CALLER: Uh, police, please.
911 OPERATOR: Can you tell me what happened?
CALLER: While I was out walking, a woman jogged by and grabbed my purse.
911 OPERATOR: Can you give a description?
CALLER: Yes: It was a she.
911 OPERATOR: Please hold the line while I transfer your call to the police.
click click click
OFFICER: Can you tell me why you're calling us tonight?
CALLER: Yes. While I was out walking, someone grabbed my purse away while running.
OFFICER: Can you give a description?
CALLER: Yes. It was a she.
OFFICER: Okay...we've been getting a few calls about her lately. I guess I'm not supposed to tell you this, but about two hours ago, she was spotted breaking into a car. About 20 minutes later, she left a convenience store without paying for her purchases. And now we have her purse-snatching.
CALLER: I hope I can be of some help.
OFFER: Oh, you have been. With the description you've given us, we have a much greater chance of catching the perpetrator than we might have otherwise.