I agree with the Supreme Court on some cases and I disagree with them on others, but overall it is appealing to authority if we say something is constitutional or unconstitutional because the Supreme Court said so. As an example, I disagree with the decision Roper v. Simmons (2005), which declared 18 as the minimum age of execution. The Court decided that individuals under 18 do not have the mental capacity to understand the gravity of their actions enough to deserve being executed. I don't agree with that, if a teenager was able to decide to commit a murder and carry it all the way through, then they definitely had the mental capacity to comprehend the consequences.
The supreme court is a collection of individuals with degrees in law - not necessarily constitutional law. Supreme Court decisions can and have been revised, such as the Dred Scott Decision. Any person that uses the argument that somebody designated with that said so is appealing to authority and not using any logic of his own, or even defending the source itself.
No, stating that something is Constitutional because the Supreme Court said so is not an appeal to authority as the Constitution lays out that the Supreme Court has this authority and function. The Constitution sets the Supreme Court as its ruling body, so to speak, so it is now a philosophical appeal to authority to cite the Supreme Court.