I'm not being facetious at all, but you are ignoring the real reason. I'll do my best to take you seriously and change the example from rocket launcher to fully automatic machine gun, which is a distinction without a difference to my point. They are not hard to conceal, and only rare because they are regulated to the extent that there is not a significant non military demand. They are still expensive, of course, but that's not the real point.
The point is that it is perfectly legal in the United States to own a machine gun (or a rocket launcher for that matter) with the correct permit. However, that process is justly and reasonably stringent enough as to ensure that the permit recipient is incredibly unlikely to use the machine gun in an unlawful way, or to be callus enough to allow that gun to be lost or sold to someone who would. Add to that the penalties for Illegally possessing or converting to a fully auto is sufficient enough as to serve as a significant- if not absolute- deterrent.
Should a handgun require the same permitting process as a full auto? I don't think so. But somewhere in the middle of a class III FFL and virtually nothing would be cool.