Are you referring to the taxpayer support of state (not private) colleges, which subsidizes the tuition of in-state students? Foreign student don't get that subsidized rate.

Or do you mean the taxpayer-supported research - that anyone with an internet connection can download the results of, from anywhere in the world, without paying a penny of tuition?

If we were to compare it to a transaction, I think something like California exporting alfalfa to Saudi Arabia might make more sense. We've only but so much water to use and it's far from absurd to question if it makes sense to let our limited resources get drained for exporting things elsewhere.