What is surprising is that usually sensible commentators such as Chris Hayes on MSNBC also have expressed such concern, as has the ACLU. Let's, therefore, unpack this issue.
Placement on the no-fly list indeed happens with no due process. Anyone placed on this list can of course protest the placement, and be removed from the list, but this could certainly result in months or longer of the inconvenience of not being able to fly. So why do we do this? Because we think the danger of a someone flying a plane into the equivalent of the World Trade Center is so grievous that it merits this placement on a no-fly list without a trial or hearing. And, again, such placement is not permanent, because it can be removed. John Lewis, who led the brave sit-in the House of Representatives last night has himself been mistakenly put on the list and been removed, as has Yusef Islam aka Cat Stevens (who recorded "Peace Train").
As we've seen most recently in Orlando but tragically in too many other places in the past few years, an assault weapon may not be able to do as much damage as a plane flying into a building, but it can kill dozens of people in almost the blink of an eye. Surely the keeping of such weapons out of the hands of terrorists and other suspected potential killers is a worthy and reasonable goal, which is what the suggestion of preventing people on the terrorist no-fly list from buying guns is all about.
If denial of due process is the concern, than the terrorist no-fly list itself can be examined, with an eye to how and why people are placed upon it, and what they can do get their names removed. Certainly making that process much efficient and accurate is a goal that everyone should support.
But tying gun control into it makes no sense and is a red herring. A no fly/no buy list may indeed be a case of shooting first and asking questions later - metaphorically. But it's the least we can do to put a dent in terrorists and other maniacs horrendously actually shooting first and authorities asking questions later, which seems to be happening almost every day now.