Moreover (and this is a purely libertarian argument- neocons hate since it undermines their entire raison d’etre), free trade has been shown to be the best way of spreading freedom of any in history. There is an increasing amount of evidence to show that free trade leads to increased freedom of speech, a more vibrant civil society, and more stable politics. A decent primer on this can be found here:
http://www.econtalk.org/archives/2008/04/coyne_on_export.html

It’s frankly common-sense, when you think about it. The more widespread the contacts a country has with a liberal democracy, the more that country will be able to observe the benefits of real freedoms. If, however, you limit trade (and therefore contacts) with that country, or if your contacts are primarily associated with violence and political instability (ie, you invade them militarily), then people in the other country will have no basis upon which to form an opinion of liberal democracy. Similarly, if contacts with another country are limited to contacts associated with violence and instability, then liberal democracy will not appear to be such a wonderful thing.

Just one good example of this can be found in Mexico. While I am not arguing that Mexico is perfect or is even a particularly liberal country, the fact is that it has become much more liberalized in the 15 or so years of NAFTA than it ever had been previously. Prior to NAFTA, it’s worth mentioning, Mexico had single-party rule for something like 80 years (not sure about the exact number). Not long after NAFTA, though, you suddenly had reformers getting elected. Now, the biggest threat to freedom in Mexico (as, btw, is the case in Colombia) is our idiotic War on (some) Drugs.

Another example, despite its ongoing human rights abuses, is China. While those abuses continue to be unconscionable, there is absolutely no denying that the country has become more politically open in the years since detente and trade reopened with them. That progress has been ongoing, albeit slow. But I don’t think there’s any argument that the country is more liberal by orders of magnitude than it was under Chairman Mao.

Finally, I would point out that the least liberal countries in the world remain countries with which we have had no trade relations. Think Cuba, for example, which has gotten no better in almost 50 years of trade embargos on our part. To be sure, it has trade relations with European countries, but those relations are somewhat limited due to Cuba’s distant proximity from Europe. Were we to end our embargo of Cuba, in all likelihood that country would begin to liberalize politically quite quickly.