Without exit immigration, none of our airports are configured in a way that makes this workable today. There's nothing stopping someone in transit from just walking out the door.

Some airports are designed in a way to quickly facilitate this if the government ever changed its mind (IAH and LAX TBIT, I believe), but today none of our airports are set up for international sterile zones.

From the perspective of an American departing internationally, this is a bonus since you don't have to wait in line for exit formalities.