The whole idea behind NAFTA supported this free market economy idea, where all countries involved could trade more openly. The result was not the intention, but that was the idea. Having similar commercial laws makes it less difficult to manufacture and ship products to foreign countries. For instance, there are different windshield requirements in the US and Europe as it pertains to cars. That means that different windshields will have to be created depending on where the car is intended to be sold. This is unnecessary.
If they did, trade could flow more freely. This would also help us fight countries like China,who have gained too much power through trading. We are forced to deal through pacts, rather then having free flowing. The world needs to have more trades come easy, not through pacts or fear of war.
Making international sales contracts can be difficult since even though a contract can specify a the laws it is to be governed under there is still going to be super ceding laws in each country with, as an example, regard to doctrines of fairness. Making those laws similar makes worrying about such issues trivial.
I believe international trade is quite easy, especially given the openness of the Internet. I believe countries and the people in those countries can benefit from international trade, but if the country doesn't support it at this time, it is likely there are more problems in that country, outside of international trade abilities.