> We don't need to know the rest of it, or if we do, it should be surveyed separately with voluntary participation.

But we do. A detailed census is essential for making good policy. For example, knowing the age and distribution of children across the country helps local and state governments decide where to put the next school or children's hospital. The federal govt. allocates funds for education and daycare accordingly.

The census is the best and most important measure of govt. policy. Taking it away would leave everyone worse off.