And what do we get in return? An illegal invasion of all of Central and South America's human debris. They are treated better than our military vets. We are a debtor nation to Mexico in more ways than just 'trade deficits'. But through 'trade' agreements we could in a heartbeat build a wall... and Mexico would indeed pay for it.
Uhhh... oil and food.
And what do we buy it with? Our Federal Reserve quantitatively eased fiat dollars.
I think someone else answered that question well and I cannot add to it.