Compare Huck's conversation with Buck with the conversation about killing among Huck, Tom, and the other boys in Chapter Two.

Huck's conversation with Buck is about killing for honor, albeit a forgotten honor, while the conversation among Huck and the other boys is about killing because that's what robbers do.

Both conversations are about killing for principle.

Explanation:

Buck told Huck about the feud between his family and the Shepherdsons and explained why he has got to kill any he comes across because of it, but he doesn't know the reason why, he just knows he must "Why, nothing-only its on account of the feud."

When Huck was with the gang of boys they talked about robbing people and killing them, because "Oh certainly. It's best. Some authorities think differently, but its considered best to kill them-except some that you bring to the cave here and keep them till they're ransomed."

The two conversations are both about killing people because they think they must kill people, without actually knowing the reason why they must do so. In the one with Buck and Huck, its killing due to the feud even though no one knows what it was about.

In the conversation with Huck and the other boys, it was killing because killing is what robbers do, there's no reason why.