As Huck and Jim get closer to what they think is Cairo, Jim grows increasingly excited and Huck grows increasingly anxious. Huck feels an extreme sense of guilt as it kind of dawns on him that he is essentially helping a criminal, from society's point of view. On page 113, Huck is thinking to himself and finally decides what he truly thinks about the situation. "S'pose you'd a done right and give Jim up. Would you felt better than what you do now? No, says I, I'd feel bad-I'd feel just the same way I do now." Either way Huck is going to experience guilt and, for now at least, he chooses to continue on his journey with Jim.
In Chapter 18, Huck stays with the Grangerford family for a while. I thought this part was interesting because he meets this family and the first thing he finds out is that they are in a feud with another family, the Shepherdsons. Because the feud has been going on for so long, each family feels like they have a social responsibility to kill the other. It doesn't matter why the feud started any more-they are bred to hate each other and are taught that it is the right thing to do. When Sophia Grangerford runs off with a Shepherdson boy, it causes such a stir that it results in a full-on battle and the death of two Grangerfords.
These two specific scenes show social responsibility in a different light than you would usually expect. The technical "right" thing to do in both situations is not necessarily the obvious choice. Turning in your friend and killing people you have a grudge against are both examples of what specific societies felt are a responsibility, but they're things that our modern day society would definitely consider wrong. And because Huck has never cared much for doing things just because he is "socially obligated" to do so, he enters both of these situations with a different point of view (that is actually more similar to a modern point of view), and he is the one who would be considered wrong for the decisions he is making.
