U.S. Rep. Ron Paul (R-TX) provides the short, easy-to-understand, impossible-to-ignore version of why CAFTA should be sent to the scrap heap. From "CAFTA: More Bureaucracy, Less Free Trade":

...The quasi-judicial regime created under CAFTA will have the same power to coerce our cowardly legislature into changing American laws in the future. Labor and environmental rules are inherently associated with trade laws, and we can be sure that CAFTA will provide yet another avenue for globalists to impose the Kyoto Accord and similar agreements on the American people. CAFTA also imposes the International Labor Organization's manifesto, which could have been written by Karl Marx, on American business. I encourage every conservative and libertarian who supports CAFTA to read the ILO declaration and consider whether they still believe the treaty will make America more free.

CAFTA means more government! Like the UN, NAFTA, and the WTO, it represents another stone in the foundation of a global government system. Most Americans already understand they are governed by largely unaccountable forces in Washington, yet now they face having their domestic laws influenced by bureaucrats in Brussels, Zurich, or Mexico City.

CAFTA and other international trade agreements do not represent free trade. Free trade occurs in the absence of government interference in the flow of goods, while CAFTA represents more government in the form of an international body. It is incompatible with our Constitution and national sovereignty, and we don't need it to benefit from international trade.