US Government doesn't trust academics. Fears that dangerous knowledge will get into the hands (and brains) of the Enemy. The notion of "export" is stretched to include knowledge transfer into the heads of scientists who are not US citizens. Foreigners are to be discouraged from visiting sensitive research facilities; US scientists are to be discouraged from employing (or talking to) non-US graduate students and research associates.
This is the fortress model of security, implemented by restricting normal traffic.
So academics don't trust the Federal Government. (See this piece from Berkeley.) Wary of measures that will restrict academic freedom. Don't attend meetings from which foreigners are banned. Advising regular disclosure: give your findings away before the Government stops you.