Like Rubashov, Ivanov also has some misgivings about the direction the party has taken and he makes the mistake of revealing them to his deputy at the prison. The deputy is more direct in his sinister behavior. He has no illusions of serving the people. To him, the ends justify the means. There can be no opposition to what the party says, as personified by No. 1.
Any minor dissent is treason deserving of the ultimate penalty.
Most of the characters in Darkness at Noon remain relatively unfurled. Alas, such a conversion is probably impossible for the old Bolshevik. Rubashov is likely not lamenting his own demise at the hands of a corrupt party, just the fact that the party's plan was not followed by the right people. Of course, today it's become a familiar lie. We last heard it with the collapse of socialism in the old Soviet bloc - the system didn't fail, it was the people who tried to institute it.