" But if you are a student from one of several countries, you need no visa and you can enter the USA multiple times during a ten year period with no problem:"
I am missing your point - other than this is and has been a problem for a long time.
Certainly anyone not living under a rock knows our immigration laws and policies are in need of drastic revision. Perhaps this particular policy needs imminent review lest we risk bringing in sleeper cell trainers or instructors under the guise of "education." At the very least, security checks need to be done on these people, prior to them setting foot on American soil. IMHO we cannot be too careful when it comes to foreign nationals entering our country and blending into the environment here.
Sleeper cells represent a clear and imminent danger to us all. We need to inhibit their contacts and remove them and anyone who assists them from wherever in this country they exist. That is my point Bobibutu.