In our legal environment, due process means a finding by a judge or jury in a process where the person has the right to counsel, to confront accusers, discover evidence, etc.
We already have that in place for firearms sales. A person who is adjudicated mentally ill cannot legally buy or possess a firearm or ammunition.
It is legally and morally impermissible to deny a person the right to keep and bear arms or any other right simply because enough other people think he's weird. I'd be the first to go in that case.
And, as you rightly understand, if bureaucrats could deny a right without due process, an anti-RKBA administration could put any number of people on the list. We have already seen that kind of problem with the no-fly and terrorist-watch lists.
Crazy people are going to do crazy stuff. If they cannot obtain what they want legally, they will steal it, buy it on the black market, or find an alternative.
In the Tucson massacre, if the lunatic absolutely could not have obtained a weapon, he could have done his evil deeds with an SUV or stolen garbage truck (Tamie beat me to it). China currently has an epidemic of knife attacks, often with multiple fatalities before the cops intervene. The worst cases of domestic terrorism in U.S. history have been accomplished with explosives, not firearms.
- Jim