Their better natures.

[Yes, cute is definitely the right word to describe her optimism.]

Anyone who would go for that is likely to respond anyway. The ones who wouldn't are likely either too scared to think clearly, or the ones who truly don't care about anyone but themselves.

[Or anyone beyond a small circle of people--which would be the group Rip falls into.]

Appeal to their common sense before you try their common decency. You'll likely have much better luck.