Inspired by something I do, named by this trope.
In order to make the proper choice, all options must be conceivable. If something is impossible, that is one thing, but convincing oneself it is impossible because it is immoral despite being the best option is something else entirely.
Simply giving oneself permission to think these thoughts can seem too far to go. After all, if you can think these things, you might do them! Despite the fact that I disagree, I understand the sentiment. So here's a workaround: Set aside a part of your mental processing to argue the evil side. You can make that anything, e.g. just giving yourself permission to think the thoughts--probably one of the best options--or creating a character to argue the side. Remember those shoulder devils from cartoons? Those work. I personally prefer a femme fatale, her male counterpart, or someone else who's going to be wearing a lot of immaculate black and have that aura of deft intelligence.
Discussing this feels weird. What I am describing is sitting down, seeing the little devil complete with pitchfork and smile pop up on my left shoulder, and then listening. If seeking some solace, one may look for an angel and completely miss the point when finding none. If there are only two of you, and you can't see the angel from a first-person perspective, who do you think you are? The point of creating this mental construct and listening to him/her/it in the first place is to allow thoughts to go into places they wouldn't go before. And even with the adviser in place, that is not the part with the final say. The composite gets the final say. A common trope about evil's weakness is that it cannot comprehend good. The strongest good mind is that because of an ability to entertain evil or "evil" thoughts, and then choose good anyway.
I'm not claiming to be the strongest good mind; I've never been in that extreme a situation. But I do not believe truly good people have been good out of ignorance.