Valid.

Before 9/11, the Bush administration had several clear warnings that something serious was in the works, and they totally ignored it. It was even put into his daily briefing that Al Qaeda was planning an attack that involved flying planes into buildings, but it was later speculated that bush probably never even saw it, since he often skipped reading his morning briefings.

If they had stopped to consider it, they would have realized that they had been receiving reports from flight schools of Arab students wanting to learn to steer planes in flight, but not take off or land, and one guy already in custody. Just a little bit of investigation would have exposed the whole thing.

But they wanted a Middle Eastern conflict, so all of it was ignored, with easily predictable results.

A False Flag event? Not by precise definition, but essentially the same thing.