In all honesty–and I say this as a pilot with both FAA (U.S.) and JAA (European) licenses, I have difficulty in seeing what makes this such a problem from the security point of view.
I take it that what we’re concerned about is preventing another 9/11: ill-disposed people getting hold of commercial aircraft and using them as weapons. Light aircraft–your Cessna 172s and the like–are not a concern because they weigh less than a Toyota Tercel, and can carry even less of a payload. One could certainly stuff one of them full of explosives and fly them into a building: but less damage would result than doing the same with a mid-size Ford and parking it outside in the street.
That being so, it’s hard to imagine how imposing additional scrutiny on _ab initio_ flying schools will make anything or anyone safer. (And even if the object of the exercise is to keep foreigners away from Cessna 172s, such foreigners, assuming they have done their training overseas and have already got a private pilot’s license from a country that is a member of the International Civil Aviation Organization, can perfectly legally come in on a tourist visa, call around to the local FAA Flight Standards District Office with their documentation, and obtain a temporary airman’s certificate that will entitle them to rent and fly U.S.-registered aircraft for the duration of their stay.)
Nobody wants people with evil intent flying any sort of aircraft, large or small, of course. But neither does anyone want them renting Ryder trucks, stuffing them full of home-made explosive, and parking them in the basement of the World Trade Center (remember Ramzi Yousef, 1993?). The time and place to scrutinize them is at the border when they first present themselves for entry. Otherwise, the focus must be on ensuring that baddies do not get access to the sharp and pointy ends of commercial aircraft. Banning all foreigners from U.S. flight schools will do precisely nothing to make that more likely.
