I have a hard time believing the guidelines could be successfully challenged in court on their own merits; they are basically justification for the copyright holders to pursue legal action should they choose to do so.I tend to agree. But it it is a weak point if anyone ever tried to challenge the guidelines in court.
Well, I know of cases where "advisory" guidelines have been declared illegal. One thing to keep in mind about the FTC Act is that it's unnecessary to demonstrate actual harm. A hypothetical harm to "competition" is sufficient for agency action.
I'm curious: In your FTC example, was the agency that promulgated the advisory guidelines legally authorized to regulate the industry in question? Because that creates a formal relationship between the agency and affected companies. But there's no parallel relationship between CBS/P and fan productions; CBS is quick to point out the guidelines are not a license.
And with regard to the FTC Act, the "competition" to which companies are entitled in our society does not extend to filmmakers engaging in an act to which they are not legally entitled, to compete with copyright holders using the studios' own intellectual property.