I don't think that is the argument. Calling a cow a pig doesn't make a cow a pig. Calling a silencer a firearm doesn't make a silencer a firearm.
A "My Pillow" would a silencer if I intended it to be such and used it as such. I would argue a silencer is a flash suppresser. That's my intention and the intention is reasonable.
I believe the argument being made these days is a silencer is a safety devise or hearing protection devise. A reasonable intention.
In 2015, Los Angeles County sheriff deputies recovered a Sa vz. 26 submachine gun with an automobile oil filter attached.
Weingarten, Dean (November 27, 2015). "Homeless Man's Black Market Submachine Guns and Improvised Silencer". thetruthaboutguns.com.
PVC pipes
Workbench Silencers: The Art Of Improvised Designs.
plastic water bottles
Emerson, Clint (Oct 13, 2015). 100 Deadly Skills: The SEAL Operative's Guide to Eluding Pursuers, Evading Capture, and Surviving Any Dangerous Situation.
foam-filled pillows
Itabashi, Hideo H. (2011). "Injuries Due to Firearms and Other Missile-Launching Devices". Forensic Neuropathology: A Practical Review of the Fundamentals.
however, yes these items and others are illegal to use as a silencer/suppressor/etc. and must have a ATF Form 1 and the ATF's privilege stamp... >>> earlier this year ATF raided Diversified Machine because the ATF determined that Diversified Machine was manufacturing what the ATF felt constituted a suppressor and selling them to individuals.
themachinegunnest.com
but know CoL i promise won't snitch on you for hiding your silencer pillow in plain sight...now where did i put the ATF's informer fone ##