Most of the Jedi had no reason to expect order 66 would happen.
It doesn't take a ****ing genius to know that betraying the Jedi, putting Dooku and Ventress in the same ship, and planning on hunting Darth Sidious, and expecting to live a peaceful life with Ventress afterwards just wasn't going to work. He didn't do it for philosophical reasons, he did it because he wanted to **** Ventress.
Krell betrayed the Jedi because he wanted to be on top when the empire took over, and the guy thought betraying the Jedi in the heart of their army and taunting the people with guns to his back were good ideas.
And Barriss thought the Jedi "losing their way" was moral justification for killing civilians and terrorism.
TLDR: Vos is a selfish ****, Krell is an ass, Barriss is just wrong, and all three of them are philosophical failures.