A couple of points not mentioned before someone took their toys and went home...
The "long standing" prohibition against felons and the mentally ill (on the Federal level) was enacted in 1968. Prior to that, there were no blanket prohibitions on felons owning firearms AFTER THEY SERVED THEIR TIME, and all other conditions met (parole, probation, etc.)
A mentally ill person is (and always has been) prohibited, on an individual basis, and only AFTER due process. Even the 68 law recognized this, and requires adjudication by a court, before firearms rights are denied to the mentally ill. A doctor's opinion alone is not enough. All your family saying you are crazy is not enough. It takes a court hearing, where both sides testify under the rules of evidence, and a court decision.
This is NOT the case with convicted felons today. Denial of the fundamental right to arms is now a blanket prohibition FOR LIFE, if you are convicted of a felony or "domestic violence" misdemeanor.
Lots of people in this country have done something (usually in their youth) they shouldn't have, and got convicted of "felony stupid". (meaning something that resulted in little or no serious harm, but was classified as a felony). Those people are automatically banned for life. Some of them, perhaps, should be, but there are a lot of people who straightened up their lives and have spend decades, even several decades without any legal troubles at all. Yet, despite 20,30, 40 or more years being good citizens, they are still banned for life.
There is, technically, an appeals process. However, on the federal level, at least, somehow, the government has neglected to FUND that process for many, many years, so while it technically exists, in practical terms, it does not.
The other point is one brought up several times, about how a UBC system cannot be enforced without comprehensive registration.
This is not entirely true. It could be done. It won't be, because the people pushing UBCs don't want it done, and won't accept a system that doesn't need full gun registration.
The way to do it is deceptively simple. Take the gun out of the equation.
There is no need for it at all. You simply check the PERSON, not the gun.
There is no valid need to check the gun at all. The stated point of the background check is to verify if the potential buyer is, or is not a prohibited person. (right???)
IF that is actually the case, as the prohibitionists say it is, then the specific gun doesn't matter at all. CLASS of gun matters a tiny bit, because of Federal age restrictions, but the actual gun by ser# is useless information in determining prohibited status, or not.
UNLESS your goal is to create a registration system, then, it is vital information.
One could, (and probably with less effort than the current and proposed UBCs) check every adult in the country for prohibited status, and mark it on their driver's license or ID card. Then, all that would be needed for purchase of a gun, ANY GUY, is a check on the PERSON to see if the status on their ID has changed since it was issued.
So far, everytime something like that has been proposed, the prohibitionists have flatly rejected it. Since it would do the same thing (prevent prohibited persons from purchase) as their systems, but without any kind of gun registration data, one does have to wonder, WHY they oppose it so strongly.
Could it be that their true intentions are not what they publically claim them to be??
Or that they don't like to admit what their true intentions actually are??