Social security number is not a national ID. THe cops cannot stop you on the road randomly and ask you to prove your identity. That is illegal in the US, UK, India etc. Social security number is fine... make the PAN number cumpulsory for all, that's ok. This is different. This requires you to carry a piece of paper on you all the time. If you lose it or forget to carry it and are stopped by the cops, you are in serious trouble right? Isn't it just one more tool for harassment?