Social Security Numbers - What do you know?

I never really understood why the US rely so heavily on a SSN. You have a number that's used for pretty much most important dealing with the governance, taxation and stuff, and yet you seem to have to use it all the time, as an authentication method, knowing full well that most cases of identity theft occur with the help of a SSN. Aren't there any other ways that can be used to authenticate a person, instead of asking for apparently pretty important personal information? Do you people feel safe with this method?

Jam it back in, in the dark.