Re: Americans dont understand that, though

Mostly avowed conservatives, yes.

Yet I have only heard the most extreme liberals advocating leaving the Americas back to the Native-Americans (and the rest of us back to Europe, Africa or Asia, depending where our origins are).

Advocating against immigration today without simultaneously advocating for Return to the Old World is neither conservative nor liberal, but simply incoherent.

Perhaps in theory, but in practice states can't be trusted to draft and enforce "free trade" agreements. Their very involvement is antithetical to free trade.

Well yes, in practice FTAs are Wilsonian projects of "the red tape to end all red tape". But at least some trade is more freely undertaken after an FTA than before it. Even the bleeding-hearts who constantly complain about labor or environmental standards abroad magically forget that FTAs can be used (and has historically been used) to bring up such standards in the partner countries. Absent such an agreement, no obligation to be clean or to offer safe workplaces exist.

That's why the same politicians who support NAFTA also supported, say, the embargo on Iraq without blinking.

Apples and oranges. The relations of the USA with Iraq, for any number of reasons, are different to the relations of the USA with Canada and Mexico. If you want to compare Iraq to the Gulf countries, Iran or Syria, it's fair. But the only thing Iraq and Canada have in common are their vibrant Kurdish communities, and the only thing Iraq and Mexico have in common are their broad daylight kidnappings and beheadings. Everything else is different.