The ACS is NOT the once a decade census required by the Constitution. It is an annual random survey sent to about 250 thousand households every year to get data to help in decision making both by the government and private industry.
If you find some questions on the survey too intrusive then by all means don't answer them. But this is not some secret government plot and actually serves a useful purpose by providing data to support decision making.
Given the much greater intrusions that go on on a daily basis e.g. TSA searches, NYPD stop and frisks, holding American citizens in secret detention centers without charge, due process, or probable cause, this is not what I want Congress to focus on.