Blue Train,
In 1933 oranized crime was out of control. The big push for some type of control on firearms came when a 12 year old Chicago girl was killed by stray machine gun fire. There was also Bonny and Clide, the St. Valentine's day massacre, Machine gun Kelly and a host of other trouble makers.
Yes, silencers were fairly common before 1934. Most were purchased by hunters.
There was little regard given to hearing loss in 1934. It was considered just a normal part of aging. We now know that hearing loss is caused, in most cases, by exposure to high sound levels. OSHA, the EPA and other Federal and state agencies now issue noise level standards. There is no exception given to firearms, however, gun fire is noted to be at 140db or more at 3 feet from a gun barrel. Today, almost all shooters use some type of hearing protection but that doesn't help someone who happens to be near by when a firearm is discharged. I'm sure you are all aware of how hard it can be to find a shooting range these days because of the noise problems it causes for people that live near by.
When the NFA was debated, game wardens jumped in with the request to add silencers to the list of controlled items. It was the Great Depression and poaching was out of control. People were hungy. The NFA has been re-visted twice since 1934. It was modified in 1968 and again in 1986.
There are electronic listening devices made today that can detect gun fire (supressed or not) that are cheap and available. The need to regulate silencers simply no longer exist.
The question is: Do we want to change the law and what would the consequence be?