How does Twain begin to question the morality of slavery in this chapter?

Basically the new judge in town refuses to give custody of Huck to Judge Thatcher and the Widow, despite Pap’s history of neglect and abuse. This of course makes us question the wisdom and morality of self-righteous public servants who put their own biases ahead of common sense. This is also representative of the whole idea of slavery in the South as a whole.

Twain uses one of Pa's tirades to truly introduce slavery into the novel. By using Huck's father, his tirade against the slaves, the government, and some of the freedoms that were being given to the slaves throughout the country, he makes slavery seem dirty and wrong. His choice of character (Pa), who we don't like as a person, enables us to see the way Twain questions the morality of slavery. The man was a master!

"Oh, yes, this is a wonderful govment, wonderful. Why, looky here. There was a free nigger there from Ohio -- a mulatter, most as white as a white man. He had the whitest shirt on you ever see, too, and the shiniest hat; and there ain't a man in that town that's got as fine clothes as what he had; and he had a gold watch and chain, and a silver-headed cane -- the awfulest old gray-headed nabob in the State. And what do you think? They said he was a p'fessor in a college, and could talk all kinds of languages, and knowed everything. And that ain't the wust. They said he could vote when he was at home. Well, that let me out. Thinks I, what is the country a-coming to? It was 'lection day, and I was just about to go and vote myself if I warn't too drunk to get there; but when they told me there was a State in this country where they'd let that nigger vote, I drawed out. I says I'll never vote agin. Them's the very words I said; they all heard me; and the country may rot for all me -- I'll never vote agin as long as I live. And to see the cool way of that nigger -- why, he wouldn't a give me the road if I hadn't shoved him out o' the way. I says to the people, why ain't this nigger put up at auction and sold? -- that's what I want to know. And what do you reckon they said? Why, they said he couldn't be sold till he'd been in the State six months, and he hadn't been there that long yet. There, now -- that's a specimen. They call that a govment that can't sell a free nigger till he's been in the State six months. Here's a govment that calls itself a govment, and lets on to be a govment, and thinks it is a govment, and yet's got to set stock-still for six whole months before it can take a hold of a prowling, thieving, infernal, white-shirted free nigger, and -- "