Quote of the Day - What you don't know won't hurt you.
This FindLaw article on CNN explains it in great detail. As does the ACLU site above (with 138 different articles if you search "Matrix" at the top of the page).
The MATRIX gathers all types of private, government and commercially available information about you. This information could include "credit histories, driver's license photographs, marriage and divorce records, Social Security numbers, dates of birth, and the names and addresses of family members, neighbors and business associates."
The standard arguments:
PRO: Why would you mind this, if you don't have anything to hide? Why do you care if you're a suspect, unless you're guilty?
and CON: If you have nothing to hide why would you seek to enforce your privacy rights, or rights against self-incrimination, or right to an attorney? are being made.
Congress previously shut down a similar program called TIA, or Total Information Awareness, and opponents argue that the MATRIX should be shut down too.
If gathering all of this online information in one place is bad, why isn't the gathering of the separate parts of this information online equally insidious?