FYI: the TIN is a unique number associated to each person living in Germany. New born babies are getting a TIN faster than most of the congratulation cards... It is issued by the tax authorities and as a foreigner living in Germany you also get one.
In Portugal usually you always need to present you ID card and Tax ID together when some form of identification is required.
To the point that the actual ID cards (Ausweis) have the citizen ID, tax ID and social security ID all together.
Identity is a right that government must warrant, not something dirty that should be buried.
I literally just explained how it's not.
> There are no practical negative consecuences
Assuming an ideal, benevolent government.
(Presumably residing on an infinite frictionless plane, feasting on spherical cows.)
While IDs do have negative consequences, I see zero downside in replacing VATIN, passport number (linked list of "previous document" in worst case, down to birth certificate), army id number, employment record book number and "$surname $name $patronymic, born $birth_date at $birth_place, registered $registration_place" official title with single citizen ID.
I am not arguing for using government-issued IDs for non-government services (as in original post), and consider enforcement of such use a direct attack on citizen freedom, but only for having single ID for use in state-person relations.
Not in all countries. Germany used to have explicit laws against combining state and federal record bases, they were only recently eroded to "fight terrorism".
BTW, shame on Chrome for allowing it without a warning :-/ Firefox totally refused to connect.