THis is one area on which there is a broad agreement among most economists. Free trade is a good thing. If you believe in the market(ie. you're a capitalist), its very difficult to oppose free trade. Restricting free trade is essentially disrupting the free flow of goods and services. It is interfering in the natural market process, which is harmful to everyone.
In practice, adopting free trade can have negative short term consequences for some groups but will lead to much greater long run benefits for everyone. It is useful to think of things backwards. Imagine a world in which goods and services are traded freely. Now lets start restricting trade by erecting barriers. Suppose the US no longer trades with the rest of the world. Is anyone better off? No. Now, lets take California. Suppose they no longer trade with any other state. Again, is anyone better off? Of course not. Now, suppose San Francisco decided to cut off all external trade... and so on. Everytime you restrict trade, you are worse off. This is true under just about every economic model. In fact, it is very difficult to construct models under which certain parties become better off as a result of restricting trade and it is virtually impossible to construct one in which everyone is better off.
Bottom line - Free trade is a good thing. For all countries!