"If they aren't capable of handling their own business, they probably couldn't fill out the forms needed to buy one from a FFL or the ability to coherently look for a private seller in a free state where they both should be living."
Don't discount your opinion so readily, as what you've said here could very well be the truth for a large number of these folks. But I'm glad you realized that that is not the issue here; it's that whether or not these folks should not have guns or not, extra-judicial mechanism described so far is not how we debar our citizens' rights in this country. I'd much rather the administration do the honest thing here (ha!) and propose legislation to do what they desire, since that would be going through the proper channels (and even then, it would likely entail some sort of mandatory review of mental health when SSD folks file for a fiduciary, to determine if that status truly does warrant their disarmament).
What I'm saying is, to play Devil's Advocate; if we are going to try to restrict people pre-emptively based on lists, it makes sense to inspect someone filing for fiduciaries for mental competency, because the act of doing this is an indicator they are unable to perform a basic function required of society (paying your own bills). It is not unlikely at all that they would require the fiduciary because they are mentally incompetent, or soon to be so (senility).
That said, the way to add that additional screening, if we truly think it has value, is to pass a law which adds it into the Social Security processes; not dictating it by pure fiat. I thought the Federal Register Act makes a move like this --which clearly creates a new process within government, and also impacts a large number of people, and also entails an expensive appeals process-- completely illegal. At best, you could argue it is a new, sweeping regulation, and put it up for (extended) public comment. You can't just 'implement' stuff this widespread just because you know the victims won't/can't fight back.
Sadly, I think that much like the ITAR changes coming soon, this is an issue too difficult to explain to get people to oppose in numbers. By the time you explain what a fiduciary is, they've lost interest (same hurdle as explaining what a 'defense article' is). Our representatives will for sure never have any interest in learning what they need to oppose here, so they'll be of no help. This is why these regulatory approaches are so dangerous; they are so Kafkaesque/Byzantine/etc. that there is no way to properly frame the problem for widespread opposition.
"The pinnacle of strategy approaches the formless: if it is formless, then even the deepest spy cannot discern it nor the wise make plans against it.”
I think the only real solution, if there is one, is to start passing (after '16) laws which prohibit broad swathes of government regulators (as in entire agencies outside the court system) from making determinations regarding firearms disability or mental incompetence. However, I doubt there is much appetite for such sanity anymore.
TCB