Terrorists don't buy legal weapons. This law only inhibits the law abiding citizen that the leftists will classify as "potential terrorists" just by virtue of the desire to buy a gun or protest encroaching tyranny.
Terrorists will buy guns if they can. They have already done so! They are legal citizens here. Many are born here.
The GAO reported this:
In January 2005, the Government Accountability Office reported that during one five-month period (Feb. 3-June 30, 2004), people designated by the federal government as “known or suspected terrorists” tried to purchase a total of 44 firearms.
Terrorists DO buy legal weapons. They will continue to do so unless this loophole is closed.
http://www.cbsnews.com/stories/2005/03/18/60minutes/main681562.shtml