What/who do you think is Twain’s biggest satirical target? Examples?

It is arguable that Twain's most prominent target for satirical treatment in Adventures of Huckleberry Finn is people who believe themselves to be acting ethically when they are decidedly not doing so.
An example of this occurs when Huck and Jim discuss stealing food from farms they pass. They talk about what Pap and the Widow Douglas have tried to teach Huck about thievery; ultimately, they feel better when they steal melons and a chicken rather than persimmons and crab apples. Huck is happy about this and feels he has made both an ethical decision and avoided eating two foods he dislikes.
Another example is when the two men in the canoe refuse to help Huck when Huck implies that his father has smallpox to keep the men away from the raft where Jim is hidden inside the wigwam. The men tell Huck to get to shore further on down the river, apparently not caring about the people that might be exposed there, because they fear for their own health. The men float a couple of twenty-dollar gold pieces over to Huck and feel good about their act of charity when all they have done is imperil others and assuage their own guilty consciences.