Your jurisdiction, unlike the traffic of the internet, is limited to your own country. And the countries you control. Which is a lot, I give you that, but by no stretch whatsoever it's all.
Also: Money trumps laws. Twice so if corporations are involved. If $evil_bastard_country wants to throw money at whoever sells them $supersecret_technology, corporations will not obey your law, they will race against each other to find the loophole. Which usually ends in the tech involved being developed abroad by those suspicious foreigners and then sold to the $evil_bastard_country.
The net effect for the US of such a ban is a loss of jobs, loss of knowledge and most of all valuable IT security information in the hands of whatever foreign country was smart enough not to be as stupid as you are, putting shackles on your own ITSEC industry.