A lot of them don't really seem insane or corrupt. Many of the situations they were involved in tend to be extremely complex and morally ambiguous. Their actions could easily be argued as justified - but because they're not the main cast, they're usually not portrayed in the best light.
I struggle to justify most of them:
Admiral Cartwright - The Klingons were in a weakened position and no longer had the resources to be a threat to the Federation. Their Chancellor wanted Peace. Cartwright had him murdered (and attempted to do the same to his daughter) and arranged for two heroes to take the wrap. Reprehensible.
Admiral Dougherty - Okay, he wanted to harness the power of the mysterious energies on the planet for the betterment of mankind. I get that. His decision to involve the alien drug dealer sadists was complete insanity however. Literally anyone would have been a better choice. Idiot.
Admiral Forrest - sort of a joke entry. In the Enterprise narrative, Captain Archer is a great and intelligent man who is appropriate for the mission to stop the Xindi. The problem is that, in the show, Archer is portrayed as being (at times) a complete and total incompetent (SFDebris) and wholly wholly unsuitable for the responsibility.
Admiral Haftel - Complete and total insensitive prick who terrified an infant so much, she literally died from emotional trauma. Killed Data's daughter, albeit unintentionally. Arsehole.
Admiral Janeway - we all watch SFDebris, we know what a lunatic she is.
Admiral Leyton - tried to conquer the Earth based on a threat that he himself engineered. Lied to the crew of a Starship to get them to fire on another Starship, killing several.
Admiral Nakamura - authorised the disassembly of Data based on the flimsiest of proposals by a man not expert enough to safely perform this task. If Picard hadn't fought this, and fought it hard, Data would have been dead. Terrible.
Admiral Nechayev - prioritised the needs of the Cardassians over her own citizens, and sold their worlds to the Cardassian Empire - a race who historically have been shown to completely overrule their own treaties and invade neighbouring worlds regardless. Inevitably tens of thousands of Federation citizens were killed, and the Feds were at war with the Cardassians mere years later anyway, rendering their sacrifice totally pointless. A stupid decision that still makes no sense.
Admiral Ross - sort of understandable, okay.
Admiral Pressman - I get where he was coming from with the Federation cloak - the concession to the Romulans who have made repeated attempts to invade the Feds regardless - is one of the stupidest things in the entire history of Star Trek. His approach - and willingness to sacrifice multiple crews - is unjustifiable.
Captain Braxton - wacko crazed lunatic with a time machine.
Admiral Satie - despicable woman, who destroyed the careers of innocent men for sick thrills.
Admiral Jameson - Loony.
Commodore Decker - tragic but still insane nonetheless.
Commodore Stocker - complete idiot.
Captain Garth - another tragic figure, but completely completely insane.
Captain Maxwell - hmmm. He was proved right at the end of the episode, but he destroyed multiple ships on the flimsiest of evidence. Far far too impulsive.
Captain Ransom - he did ensure his crew's survival, but his incineration of the innocent aliens for fuel is completely reprehensible.
Captain Tracey - Nutter.