It would be better to issue a truly unique ID for most of our official dealings, since our social security is technically only 4 unique numbers if you were issued yours before 2011 (I do assume you're not 6) and really none of the numbers are random or intended to be used as an ID. Basically you couldn't even use it for an email password now days. So protecting this number that unlocks so many aspects of our life should be very important, and printing and mailing it, in places that criminals know contain the number, is not adequate protection.