If the states were the deciders of what is and is not Constitutional you would have the same problem as you would if you let the people decide for themselves directly. 50 states are going to have just as many opinions on the matter.
Take a look at the recent example of Obamacare and several states who attempted to challege parts of it through the SCOTUS, if the SCOTUS was unable to rule on the Constitution then how would the states and Federal government resolve this issue? And not just Obamacare, but if any state has an issue with the actions of the Federal government on the grounds of the Constitution and cannot go the courts for a Constitutional ruling then how will that issue be resolved?
I'm not saying its a perfect system or that it will always result in rulings that are consistant with your opinion of the Constitution, that is not possible for anyone. But to take away the ability of the court to say what is and what is not Constitutional and to place it within the power of anything else, whether it be the states, Congress, or the President is not a better solution.
The answer to the above question, rhetorical or not, and obvious fact evident in the decision itself, is that SCOTUS was not ruling on that Constitution, but rather a great many of the members of the court were making imperial judgments based solely on what they personally believed should be the case, and rationalizing the results.
This is the result of a system based on precedent, rather than direct rulings based on that Constitution.
Even examining Chief Justice Roberts' own position, it is evident that Roberts wrote some 70% of what came to be the minority opinion, and only flipped his vote at the last minute to then write the majority opinion. As pointed out by law professor Paul Campos in a
Salon article "Roberts Wrote Both ObamaCare Opinions", it is extraordinary "in the court’s history that a dissent has gone on for 13,000 words <the first 46 pages of a 65 page dissent> before getting around to mentioning that it is, in fact, dissenting." The very idea that a Justice could flip a vote at the last minute, to only validate that legislation, on such an enormous and extensive piece of legislation that so profoundly subjects each citizen to federal dictate, is cause enough to draw the validity of that vote into serious question, and every member supporting it.
It's not as if the Constitution were some inscrutable document that requires enormous investigations into the shadows by extraordinary minds in order to establish its intent. It is actually written in an simple and straightforward manner.
Undeniably ObamaCare fundamentally and profoundly changed the nature of the relationship between the federal government and citizen, and did so, not by the legitimate means of an Amendment <which even would be extremely questionable>, but with a mere statute, is cause enough to invalidate the legislation without caveat! The fact that the legislation could not even consistently represent itself as either a "tax" or a "fine" within the legislation, and even the Solicitor General could not do so consistently before the Court, is a result of the
existing Constitutional impediments against ObamaCare under both considerations, and yet the Court did NOT truly engage either of these anywhere in the majority opinions. The claim by Roberts that there is any broad plenary power to "Tax" that is unencumbered by the Constitution and subsequent rulings, ignoring the very reason the legislation had to dance around "tax" and "fine" to begin with, is pure sophistry on Roberts' part, made solely to validate his final conclusion.
The Reality is that those Five members of the Court did NOT provide validation of ObamaCare under the Constitution, but rather did only established that the Court itself is no longer operating legitimately by that Constitution, invalidating the Court itself.
It's not anything close to a "perfect" system, but rather one which is now become thoroughly corrupt, and no longer upholding the Constitution of the United States at all, and certainly not defending individual freedom. This is not a matter of mere "opinion", but rather recognition of the fact that by ObamaCare, the Federal government usurps de facto ownership of each individual citizen, able to intrude on every aspect of their lives at its whim, invalidating the protection and due process of the Bill of Rights, to decree the relative worth of each citizen, and limit what care they shall, or shall not receive. This is thoroughly incompatible with the most fundamental and profound principles of the Constitution and the existence of any unalienable rights and Freedoms at all!
Contrary to your opinion, the Court was never intended as the final and exclusive arbiter of what is, and is not constitutional, and the Constitution itself does not establish the sole reference of all that is legitimate, but rather only the considerations that are involved in the creation of the fiction that is the federal government itself.