And make no mistake about it, THIS is the reason the gun-grabbers made them illegal and want to keep them illegal -- has nothing to do with crime prevention (effective silencers are so easy to make out of common items available at any hardware store, that anyone who wants to murder somebody quietly with a gun, will have no obstacle to doing so). The object is to make it as hard as possible for people to practice shooting, and few people will do it, and to give anti-gun neighbors an avenue for legally stopping people from practicing shooting on a simple "nuisance" or "disturbing the peace" basis, avoiding any pesky constitutional issues.
Also the reason for silencers being illegal is pure emotion, like most weapons law. They seem scary in movies. A similar thing with knives. We can’t have switchblades today in the age of the AK, because of “West Side Story” in the 50s. The Sharks and Jets scared people BAD.