The constitution says we will have a census every ten years and it is left to Congress as to what and how it is done, so get used to it.
Constitution of the United States of America, Article 1, Section 2, Clause 3:
"
Representatives and direct Taxes shall be apportioned among the several States which may be included within this Union, according to their respective Numbers, which
shall be determined by adding to the whole Number of free Persons, including those bound to Service for a Term of Years, and excluding Indians not taxed, three fifths of all other Persons. The actual
Enumeration shall be made within three Years after the first Meeting of the Congress of the United States, and within every subsequent Term of ten Years, in such Manner as they shall by Law direct. ...*"
Before I begin, I would like to remind everyone of the one of the basic tenets of law. Law states what the citizen may not do and conversely the law states what the government
may do. With that in mind I would like to draw your attention to the portion of the supreme law of our land, the constitution, that gives the government the authority to conduct a census. This law specifically mentions what information may be collected and what that information may be used for.
The first highlighted portion details that the census information is to be collected in order to allocate the number of representatives that each state of the Union will receive and also for the apportionment of direct taxes. Because the law states what the government may do, but exclusion all things not mentioned are expressly forbidden to the government. To wit, the use of census information to allocate federal funds, welfare programs or any purpose other than direct taxes and allocation of representatives is unconstitutional, or more simply
illegal.
Now, the second and third highlighted portions detail the information which may collected. This is brutally simple. The sum of the whole number of free persons. The enumeration (read counting) of all persons in the many states of this Union. No where does it state the ethnicity of the whole number of persons, the address of the whole number of persons, the names, phone numbers, insurance information, income of the whole number of persons, et cetera ad nauseam. Again that nagging little quirk of law comes into play stating that any power or authority not expressly given to the government is verboten.
The explicit writing of this clause of the constitution is very clear and well delineates that the purpose of the census is narrow and only allows the collecting of one piece of information; how many people are in each state.
In fact the only discretion that the congress possesses is the "Manner" in which this information is collected, be it person to person, by mail, by telephone. However, that discretion does NOT extend to what other information may be collected or what other purposes it is used for.*The remaining portion clipped out and represented by "..." details the number of representatives to be allocated to the original states at the time of initial ratification and the minimum population represented by a single representative.