According to Bloomberg.com, the FBI thinks that there have been quit a few cases of foreign spies getting access to American universities and trying to steal sensitive information. Not only that, but they are taught techniques that will help them get around problems faced by their military engineers back home. The FBI is trying to prevent these spies from stealing potentially valuable information*.
Then there are the unaffiliated foreign graduate students who have a year after they graduate to either get an H1-B visa, stay in school or get are kicked out of the country. If they get kicked out of the country, they forced to take their training and skills back to their home country.
So do we want the people learning valuable skills to stay and help create jobs in this country? Because it doesn't seem like it.
*Protecting our intellectual capital is important, but it's a growing world not a stagnant world. The best way for us to stay ahead is to optimize the environment for creating new ideas and new technology in our country. Right now we have a system where foreign PhD's who could join start ups or potentially start their own company are kicked out of the country, and then we have the patent issue where very recently one of the larger tech companies spends $1 billion dollars on patents instead of returning money to their shareholders or investing in developing new products.