You cannot make good people do evil things.
You have to make the evil not so bad. Like, it is just a kickback, and here is your share.
Or you just get psychopaths, who will do anything without questioning their conscience.
This is why children in tunnels will get them all hung. It is a step to far for anyone with emotions left.
My point is being "good" is not innate. People change. People can be corrupted.
Once a good person starts to be corrupted they should exit the political process for the greater good. Easier said than done though and politicians rarely exit the political process over morals.