Slavery was constitutional until the Emancipation Proclamation and attendant amendments to the Constitution. Was it right? No. Do I oppose slavery? Yes. But until laws were enacted and the Constitution was amended, it WAS Constitutional.
It was Consitutional until the Constitution was ammended. The Emancipation Proclemation was an illegal taking of property, without compensation. The constitutional thing to do would have been to in effect buy the slaves and set them free, and then proceed to an amendment. Oh the amendment could have come first, and then the problem of an unconsitutional taking would have been avoided, because that amendment would have in a very limited way, overuled the 5th amendment's protection against uncompensated takings.
The only way to make something Constitutionial, that's not, or not that is, is to change the Constitution. Abortion is constitutional, but the question was were state laws banning it constitutional. The court ruled they were not, but the Constitution hadn't changed, to make them not consitutional, only the interpretation changed. The same with same sex sodomy laws, and a host of other things.
The Constitution states that Congress shall make no law abriding freedom of speech, or of the press. This is an abridgement, Congress passed it, ergo it's UnConstitutional, and 300 pages of legalese isn't going to change that. The fact that it took 300 pages is a clue to the fact that they were pi$$ing in our boots and telling us it was raining. The syllabus (a clerks summary of the decision) went to 18 or 19 pages. Although to be fair that encompased not just the ad restrictions, but also the money restrictions and a couple of other issues.
Sure freedom of speech is not absolute, but until today "no prior restraint" was the rule, now it's shutupandtakeit. The same rule, "no prior restraint" applies or should apply to the right to keep and bear arms. Misuse of arms, or speech, can be punished, but prior restraint is not allowed, or didn't used to be, now it is. This law, and most gun control laws, are equivalent to binding your hands and taping over your mouth as you enter a theater, because you might yell fire when there was no fire. (Of course you also couldn't yell fire if there was one, a point which also applies to both the CFR law and gun control laws)