Even the American Civil Liberties Union (ACLU) thinks there's a problem using the No Fly List to prohibit gun purchases.
According to ACLU National Security Project director Hina Shamsi, "The standards for inclusion on the No Fly List are unconstitutionally vague, and innocent people are blacklisted without a fair process to correct government error."
If there is a time to adhere to our principles of constitutional due process, it's when we're reacting to horrific attacks. As emotions run high, procedural protections help us keep our wits—and our liberties.
http://www.al.com/opinion/index.ssf/2016/06/the_aclu_rightly_rejects_the_n.html