Its because the census people are part of the govern-cement.

As an instance, it would be really nice to have a group, such as the post office, where you could always update your location to collect mail.
(and they could easily keep track of people #s)

But where this goes wrong is that such an agency would share this information with "law enforcement" causing many people to not use... which are, in a great number, the people who actually need such a service.

So, remember your Miranda rights.

Everything you say can and will be used AGAINST you.

Never for you

This ends with the census takers being pretty close to asking you,
"Have you committed any crimes lately?"
"Are you planning to commit any crimes in the near future?"
"Would you please list the types and numbers of crimes?"

Or my favorite

Have you stopped beating your wife yet?