I have personally known many native Arabs and other foreign born US citizens in the Army who possessed TS clearances. From a purely personal point of view, from my years working Army HUMINT in the Middle East, it wasn't the threat of insider compromise or any other threat to national security that was a potential problem with any of these people - it was plain ol' individual integrity.

A grossly disproportionate number of them exploited their positions once they were deployed into theater and engaged in blackmarketing, extortion of local hires and other similar illegal activities. Although the majority that I personally knew of were Arab, there was also a Turk (black marketeering during Northern Watch) and a Croat (same thing during ops in Bosnia).

I say "disproportionate" - although I knew of a couple of fair haired American boys that engaged in the same thing, it was exceedingly rare. I have to say that it was the majority of non-natives that I knew in the field who crossed that line. The few that did not and executed the mission without giving in to temptation were definitely the exception.

If you're wondering, punishments in these cases were also skewed across the spectrum - from the CoC doing absolutely nothing, a unit transfer "to start over", to being PNG'ed but nothing else, or the action simply being reflected via a bad OER, to being court-martialed.