Why Use Negotiated Agreements Instead of Unilateral Free Trade?
Any democratic nation that tries unilateral free trade will find it's opposed by people who think of trade as a giveaway to foreigners. In order to prevent that, we use negotiated agreements instead. Most voters are willing to accept the possibility of gaining from exports to the other side (until they stop trusting governments).
In other words, when Donald Trump and allies criticize NAFTA or TPP on the grounds that the treaties involved are a bureaucratic boondoggle, they are offering to rescue us from a problem they caused.