Free trade requires rules. When modern nations exchange goods and services for mutual benefit they generally also seek to establish some commonly agreed rules of commerce.
These rules relate primarily to environmental and safety standards, and also state subsidies and protection for foreign investors. Think about it: why should I allow you to sell your widgets freely into my market when your widgets are not produced to the same exacting standards as mine must be under my national law? That would be unfair competition. Similarly, why should you allow my subsidised products into your market when your wares don’t enjoy the same benefit?
There needs to be some degree of harmonisation on these areas: a level playing field for competition. And establishing common rules and harmonising regulations will require compromises and, sometimes, uncomfortable trade-offs from nations.
Those rules also need to be enforceable by a legitimate legal authority. There needs to be a referee on this playing field. National governments cannot do what they like: they must adhere to the international agreements they have made.
Without those common rules, and without some legal enforcement to back them up, the system cannot function properly.
Those economic principles are a good starting point for thinking about the row over the Transatlantic Trade and Investment Partnership (TTIP), the grand commercial bargain between the European Union and the United States that is presently under negotiation.
The past two centuries of world history have demonstrated conclusively that international trade confers immense economic benefits and rising living standards.