But all countries who wish to trade internationally have an interest in having a common set of rules under which said trading takes place. Which is what the GATT, and now the WTO, has provided. And since no one will suffer more than the poor from a major collapse in world trade, the poor are major beneficiaries of the trading regime. So, if you are in favour of world peace and development, the WTO has to be seen as a good thing. As to the economics, we need to remember what trade is.
Trade is commercial exchange for mutual gain.
If both sides did not benefit, it would not continue to happen. It is precisely because commercial exchanges leave both sides better off that we all engage in them, and trade is just such exchanges across national boundaries. Which is why countries have a common interest in trade and common rules for same. It is all about mutual gain and mutual benefit. Which is why the protectionist policies of the 1930s were not only disastrous in effect, they were criminally stupid.