Let them try to prosecute someone for failing to fill out all of the extra questions and you will see the constitutionality of this law challenged.
I am reading all of this and I'm not sure I understand what all of the discussion of constitutionality of the census amounts to. I wouldn't argue that the Constitution does not define much of what and what not should be polled. However, that being said, BloodyEclipse's cite of the US Code, that is, Title 13, Chapter 5, Subchapter II, Section 141, Paragraph a:
(a) The Secretary shall, in the year 1980 and every 10 years thereafter, take a decennial census of population as of the first day of April of such year, which date shall be known as the “decennial census date”, in such form and content as he may determine, including the use of sampling procedures and special surveys. In connection with any such census, the Secretary is authorized to obtain such other census information as necessary.
makes it rather clear to me that the legal requirement to answer the questions contained in the census is included in US Public Law.
It would seem that if one wishes to be the bellweather case before the SCOTUS, one has that privilege and can exercise civil disobedience. However, until and unless that portion of the law is determined to be unconstitutional, the law requires you to respond.
I don't like it any better than anybody else.