The real concern isn't the nationality per se, it's the vulnerability to blackmail by the state that has jurisdiction over you. It's not a matter of personal responsibility, but nevertheless it has to be accounted for.

For example, I am an American citizen, but I have extended family in Russia, and I would fully expect a place like DoD to be wary of that solely on the basis that it makes me susceptible to blackmail by Russian govt agencies by threatening my family.