No buy lists are unconstitutional. The minute you are forced to sue the government for a mistaken list instead of the government forces to build a case in each instance, is when you have tyranny and presumption of guilt.
What is worse is that when an individual like the Orlando shooter happens to have a security clearance and a citizen is forces to sue the government to do its job of putting such obvious terrorist on a list, the government will not seek to take this guy on a list because in their eye the NICS checks is proof they have done their job as Congress asked them
The NiCS and no buy lists are scams. They do not stop
terrorists who have the blessings of the state
I still think there needs to be a list of people prohibited from buying firearms - but at the same time, those who are falsely on the list need to be compensated for their effort at clearing their name. And if they were put there for political reasons (similar to IRS targeting of conservative groups), then the people putting them on the list also need to be held criminally accountable.