Well, Jacen's takeover of the Galactic Alliance and legality of Cal Omas's arrest are two separate items. The former was possible thanks to the backing of the Supreme Commander of the Galactic Alliance Military and Coruscant's Senator. It's the latter that I have issues with. Jacen's loophole makes Omas's arrest and subsequent incarceration legal and I think that is the lynchpin that makes the whole thing tolerable to both the Senate and the public. The whole coup was technically legal. Cal Omas was just an imbecile about it. In a reasonable fantasy universe, the head of the secret police wouldn't be able to just enter the home of the leader of the free galaxy and arrest him without a fight. Why didn't Omas have any bodyguards that stopped Jacen from seizing the Chief of State? The Chief of State of the Galactic Alliance at a time of war has no security at all?