You're wrong. How can the SCOTUS review a FISC decision if those decisions are never made public and if, upon challenge, the government can invoke the state secrets privilege. This is exactly what has happened in the past.
The supreme court doesn't hear cases unless there are two parties. It does not issue "advisory" rulings. But if the citizenry aren't allowed to know how the FISC interpreted the constitution, then how can we possibly object and challenge the interpretation before the SCOTUS?
Further, judges don't generally do a lot of constitutional interpretation when issuing warrants. They rely on precedent. If a judge were to step a bit outside of whatever precedent existed on a given topic (for whatever reason), the person against whom the warrant was to be served would later have the opportunity to challenge the warrant, and the constitutional interpretation that resulted in its issue. None of this is the case with the FISC. They are free to interpret the constitution however they see fit without any real possibility of their opinions being challenged or reviewed.
> Of course, this isn't actually true; every sitting FISC judge was approved by the Senate, since FISC judges are appointed from the federal bench.
Nice try, but nope. Just about every Supreme Court justice has been a federal judge previously. Did that mean that there was no confirmation process? Not a chance.
Congress vetted these people to be federal judges, not members of a secret tribunal that makes secret constitutional interpretations that have the force of law and are effectively immune from further scrutiny.