You sound like yet another "10th Amendment says what i want it to person".
I've seen far too much
Person A: "Where does the constitution say that?"
Person B: "10th Amendment!"
Person A: "Um... no, the 10th doesn't say that"
the section of the constitution pertaining to the census specifically allows for other information as pointed out by a poster above who quoted the section that was conveniently left out by the Wyatt