Also it currently takes the ATF 90 days or more to process the paperwork for paying the tax, which the bill completely eliminates.
In 1934 when the law was originally passed it was intended to be so high that it would function as a de facto ban while technically only being a tax regulation that would be less open to court challenge. “As the legislative history of the law discloses, its underlying purpose was to curtail, if not prohibit, transactions in NFA firearms” https://www.atf.gov/rules-and-regulations/national-firearms-act
Let’s leave political commentary out of this and stick closely to the specific question in the OP. In particular, let’s not get into a gun control debate. No warnings issued.
As far as I can tell, it’s because they were thought of as ‘gangster weapons’ and there wasn’t anyone going to bat to keep them out of the law. The original push for the law would have included handguns and machine guns primarily, with sawed-off shotguns, destructive devices, and silencers included almost as an afterthought. During debates it became clear that there was too much opposition to include handguns in the restrictions, so they were dropped. There was a big push against machine guns and destructive devices, so the law went forward, and there wasn’t any big push to exempt suppressors and short-barreled rifles/shotguns so they stayed in. The ‘Any Other Weapon’ category is a remnant of the handgun portion as far as I can tell, since it’s basically ‘stuff that’s like a handgun but doesn’t quite fit the strict definition of handgun.’
You’re not alone. In this Washington Post article:
It states: In the legislative history, there was no discussion of “silencers.” We simply have no idea what (if anything) Congress thought it was doing about them.
The article points out that some early opposition to noise suppressors came from William T. Hornaday, who was then director of the Bronx Zoo. He argued as early as 1913 that gun technology had made hunting far too easy for everyone and that it would lead to extinctions of domestic species. His criticism of silencers was that they reduced the likelihood of nearby animals hearing gunshots, and thus allowed hunters to kill more game in an area.
His credibility was bolstered by the fact that he helped save the American Bison from extinction, which was happening because of excessive hunting. Unfortunately, he also blamed the lower classes, blacks, and immigrants for much of the problem especially Italians who were “spreading, spreading, spreading”.
But there’s no indication that his argument led to the inclusion of silencers in the 1934 law, or if there were any other reasons. They just got lumped in there somehow with grenades, machine guns, and mortars.
I suspect that some of the opposition to legalizing suppressors is due to Hollywood’s portrayal of “silenced” gunfire. The noise made by a Hollywood silenced pistol is a quiet cough, which could well be used to commit depredations without being caught. Real suppressed gunfire is LOUD, just not as loud as unsuppressed.
Attempting to covertly knock off your opponent using a suppressor is about as practical as using magnets to climb through the ductwork, another Hollywood standby. (“Thor, the God of Thunder is trying to enter my building!” – Adam Savage)
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Yeah, I would not mind the devices being put into the regular OTC firearms accessory market, really. You are just as hurt when shot with a suppressed gun as with an unsuppressed one…
I just find calling it the Hearing Protection Act cuter than it needs to be.
Gunfire from a suppressor isn’t silent; it’s still loud, maybe equivalent to an ambulance siren. So no, you’re not suddenly a gun ninja. But it does distort the sound enough to make it possibly be mistaken as something other than a gunshot. Suppressors also typically suppress muzzle flash (“flash suppressors” on rifles explicitly do this without suppressing sound) which can also make your actions a bit more covert. Another quirk of suppressors is that the ballistic crack of a supersonic round may be louder than the sound of the gun firing itself, which makes it difficult to determine where the shot came from. Listeners may be misled into following where the bullet went rather than where it came from.
All of those factors can give an advantage to a shooter concealing his actions even if it doesn’t work nearly as well as what you see in a movie.