The fact that no other major species in the Alpha and Beta Quadrants have noticed the existence of an octonary star system that was designed to be noticed seems strange, until one remembers the extent of the Zhat Vash's infiltration in other polities of the region and single-minded focus on its objective. Given the Romulan penchant for secrecy and distrust of other species, it is likely they tampered with other species' astronomical observations to keep the knowledge of the Admonition to themselves.
Additionally, space is huge. Just because the star system is there, it doesn't mean you're going to be in the right place to detect it. Enoch mentions that the Romulans consider an octonary star system apocryphal, lending further credence to the idea that the Zhat Vash has deliberately suppressed knowledge of its existence.
Everything about the "Black Flag Directive". The fact that a starship captain can be ordered to violate any law of the Federation or basic morality under threat of their ship being destroyed. Not to mention the implication that Starfleet Security can monitor any ship that closely and remotely destroy it. Bashir was right — the Federation has become more like the Romulans than they'd care to admit.
