If the FTC lacks the authority to regulate in this particular area...."
The people gave that authority to the FCC by their signup. The problem is that a judge decides to over-rule the decision of 50 million fellow Americans who have voluntarily chosen to place their names/numbers on the list those bureaucrats have offered. This judge has, in effect, said the will of the people is of no concern to him/her.
I certainly don't need to read every word of the wild-buck opinion to conclude the judge is spurring his own horse. ;-)
The U.S. constitution sets forth the process for enacting laws, and no where in the Constitution is there a provision that allows anyone (citizens and non-citizens alike) to legislate by expressing a popular view with an executive agency. If the Judge is wrong, then he will be overturned on appeal. If he is right, then petition your congressman and senator to give the FTC the authority to establish a "do not law list," and if they don't, then vote them out of office. But don't suggest something stupid like the law must be constituional simply because 50 million people (many of whom are probably not even legally eligible to vote) approve of the regulation.
That is fine, but on the other end of that list is criminal prosecution for those Co's who don't voluntarily not call people on that list.