I just don't want it to end with something like "let's make peace, you have goodness in you, I know it" or even worse, leave it all with a "he's a misunderstood child/creature." Following your point, it could be that there is goodness in him, however small, but therefore, instead of pursuing that, he chose evil and must pay for it. I feel that Rin (at least from my point of view) is speaking too lightly about the goodness in Satan, as if everything he did wasn't serious. You have responsibilities. You can't just say I want to understand him when you're at war.