Near as I can tell, the NFA 34 was passed as an employment project for a bunch of T-men who suddenly found themselves with virtually nothing to do since the repeal of Prohibition. And, as a bonus, fell in line with the agenda of people who felt any means of getting any guns out of the hands of citizens was a good idea.
if the laws have had their desired effect, perhaps all/any firearms should be treated as a "machinegun" to reduce crime
This was in part, the intent of those who drafted the act to begin with.
The original draft of the NFA 34 covered machine guns, short barrel arms (sawed off shotguns, rifles, and stocked pistols) and HANDGUNS!
Realizing that the could never get that through Congress, the act was re-written dropping the registration of handguns, and substuting "silencers" instead.
The Hughes amendment was intended to be a poison pill, to kill the FOPA, a bill badly needed to protect innocent gun owners, sportsmen and dealers from prosecution for innocent or inadvertant violations of the GCA 68 and other gun control laws, and to provide blanket protection for those traveling with guns through anti-gun areas on their way to other places where they could legally have those guns.
But it didn't work that way. Despite the addition of the Hughes Amendment, Pres Reagan signed the FOPA anyway. While this was a huge blow to legal full auto ownership in the US, there never were very many full auto owners, compared to the general gun owner population, and Reagan went for the "greatest good, for the greatest number". Perhaps, or even probably he shouldn't have, but it was done, and tis done, and there is nothing we cando about it, until, and unless we can get the law changed.
And, frankly, I don't see that happening. There is virtually no one alive today who can personally remember being able to go into a hardware store and buy a Tommygun over the counter. And those of us who can remember being able to add new (and newly discovered) guns to the legal civilian registry are getting fewer all the time.
With Hollywood brainwashing the public well, over the last 70+ years, ordinary (non NFA arm enthusiasts) truly believe that only govt agents and criminals can have machine guns.
While it may be our right, there is, and will be no public support forthcoming for even so small a step as opening the registry and going back to the pre May 1986 laws. And any effort to bring this about only serves to remind the people (and especially the antis) that there still is a small amount of legal civilian machine gun ownership in the US. Sadly, if this happens, I can only forsee us losing some of what we still have, like the fact that the $200 tax has never been adjusted since it went into effect.