"Due process" is the key phrase here: the US government should never be able to revoke fundamental liberties based on mere suspicion. This doesn't necessarily mean that suspects are entitled to a full-on court hearing, but due process does mean something substantive, speedy, and fair.
That's why I'm not comfortable with proposals to use watch lists — as currently constructed — to deprive suspects of gun rights. I think it's wrong that those lists are used to deprive suspects the right to fly.
Understand: I'm not against depriving guns or flight rights to terrorists. But there's got to be a process that's open, understandable, and lets the accused make a legitimate effort at challenging the designation.