That is the theory. I might be pessimistic, but it looks to me that everyone claims that one want that even playing field and at the same time, hides as much subsidies as possible to be able to protect ones own industries. Europe is heavily subsidizing its agriculture. The US are heavily subsidizing anything that has a link to anything military and oil. And others are doing the same. True, a few markets have been freed and commerce has increased, but an enormous amount of industries are helped by governments who like to criticize the subsidies of the others.
By the way, there was a nice article last year about how the US are subsidizing the oil and fossil fuel industries in two ways: first by direct subsidies (about $20 billions each year and the "hidden" one about the cost of carbon emissions which can be estimated at $200 billions per year (which is real money on the carbon trading market : the government pays for the carbon emitted by its industries).
(https://www.forbes.com/sites/ucenergy/2017/02/01/the-200-bil...)
It is interesting to see that the "Clean Power Plan" of the previous administration was made to allow for levelling the playing field more or less by removing those hidden subsidies, and that the current administration destroys it. And that is not even including the costs of global warming that will impact the future for todays actions.
So to sum up, the supposed efficiency of the markets seems to me like an illusion, or at least, an ideal that will be never reached because it allways allows for cheating. Same for the postal union of this topic : for years, the US had a net gain financially from it and it didn't seem to bother them. Now, it is China that has this net gain and they are not behaving differently than the US did for many years by trying to preserve this advantage.
I don't think anyone sensible would fault China for taking advantage of something that is advantageous for their businesses, nor for them to advocate for it. It would be irrational for them not to, the subsidies exist so obviously any reasonable business would use them.
Nonetheless, it's clearly not in the interest of US businesses. The US is not obligated to provide subsidies that, due to the scale of trade using this tool, demonstrably favor Chinese small businesses over those in the US and distort the market.
I'd much rather see the market made more balanced by charging the same prices for shipping than by tariffs. At least that's a real cost. Though I have the ulterior motive of thinking charging full price for air freight will reduce carbon emissions and inefficient supply chains.
USA as well, but there is a good reason for it. It's a strategic. You are 9 meals away from a revolution. Other subsidies are for strategic purposes. There are always a few abuses which you hear in the news, but the logic is sound.
New Zealand cut off its agricultural subsides and its food exports exploded. Realities of globalization include problems and trade offs but do not match this criticism.
