How well does it work?
One reason would be that universal IDs are not really suited to the task. They do not have a consistent form, and depending on how they're generated, they are all more or less user-unfriendly. They're not necessarily globally unique either (it would require an immense amount of coordination to achieve that).
Some countries might not have universal IDs at all, I bet there's not few countries where it isn't even exactly known how many people exist or who they are. Most certainly, there exist hundreds of millions of people (probably more) who do not have any such thing as an ID card, a social security number, or a birth certificate. They probably don't have much internet access either, but should we in principle deny them using websites because they lack an ID number?
The number on my ID card is 10 alphanumeric characters, and my universal ID on the backside of the ID card is date of birth reversed, plus one digit, plus 7 seemingly random digits, and a letter.
luckyguy777 are way easier to remember as usernames than
6805097<8614257D, are they not?
What do I do if I ever want a second account, or I wish to abandon an account and replace it with another? Maybe I lost the password and can't access the recovery mail address, maybe the account was hijacked, or something different.
Well, do not despair, that's easy: You only need to get another unique ID. Oh, wait...
Do you trust every website?
Another, even more important reason is you likely wouldn't want some random website to know your ID at all. It's the same thing as with biometry. Or, to a lesser extent, with email addresses and phone numbers. Your phone number is one of the first thing everybody, not just websites, wants to know. Buy a table at a furniture center, and they want to know your phone number. When you tell them "Well,... no. I don't want you to call me", they seem offended1.
Now, the thing is, in the worst case you can always easily change your mail address and phone number. Changing who you are and what you are is troublesome. Plus, ID numbers contain check digits and are verifiable, so giving a website (which won't accept a "No") a fake number probably won't work well.
Websites, and the companies behind them, are generally (with very, very few exceptions) not trustworthy. In fact, this very website (Stackoverflow to be precise) proved its unworthyness only yesterday by sending me unsolicited job offer spam under the false premise that I opted in to receive these. Sure, not much harm done in this case. But do you really trust every random website enough to give them your identification which is many orders of magnitude more sensitive than a throwaway Google address? Really?
It's not long since you only needed a name (presumably someone else's name) to rent a parcel deposit box. Welcome to the world of online fraud. Loot is sent to the victim's name, to the victim's deposit box. Only just... they have no idea they own that box at all, and they didn't order anything.
Meanwhile, you need a name and the matching identification number. I'm not sure why you still don't have to physically present an ID, but whatever.
Do you really want to tell some random website that number?
Did you think it to the end?
Universal IDs are generally a problem, more than one might think. Many of us are concerned about Facebook and Google storing a cookie and placing beacons on websites. But what if you told them your universal ID?
I remember working in a Swedish hospital around 20 years ago where you could access every person's medical record (and other personal data) by entering their unique code in a computer which, of course, didn't require a password or anything. Their unique code, that was their date of birth backwards, plus a 2-digit sequence number (or something very similar).
Also, there was a database (again without password) where you could match names, partial addresses, and age ranges to find out the number in case you didn't know and in case the patient could maybe not answer. Which is no problem because, obviously, we're all professionals, and nobody would ever use this data for anything but what's intended.
My initial thought was: "Woah, we are so retarded, still using paper -- the Swedes are so fucking cool. Compared to them, we live in the middle ages".
On a second thought, I was much less extatic with the idea. Why, it's a great thing, is it not? And you have nothing to hide. Plus, it's only ever beneficial.
Yes, except... if you knew this girl's name was Inga2 and you didn't even know her last name, but you guessed she was approximately 22-24 years old and lived in this town, then, well, you could within seconds look up whether she had a history of genital herpes before going on a date!
Not that I would ever do such a thing, nor can I confirm or deny knowledge of any circumstances under which other individual people have or might have done or recommended said or similar thing, even on a hypothetical base.
Data, and the ability to link data to people is a very, very dangerous thing, it should be avoided at all cost if you can help it. You should never let it happen voluntarily, without urgent need, and without consideration.
1 "Oh, I cannot afford a cellphone" works much better, it also limits the amount of extra stuff they're trying to sell to you.
2 Name changed to protect the innocent. Any resemblance to real persons, living or dead, is purely coincidental.