Back in the good old days (1900-1920), capsules containing tape worm eggs were marketed as diet pills, would you protect the right to do so?
Anyone who gives the issue a moments thought knows that some people are gullible or ignorant (how many of us are not ignorant in some areas) and others have no scruples what so ever. In my opinion, it is an appropriate function of government to criminalize fraud and prosecute the perps, just as it is to jail some thief who breaks into your house.
Well, they worked, didn't they. (kidding). Seriously, ensure the product is properly labeled, that's all you need to do.