From the text:
"Well, I tried the best I could to kinder soften it up somehow for myself, by saying I was brung up wicked, and so I warn't so much to blame; but something inside of me kept saying, "There was the Sunday school, you could a gone to it; and if you'd a done it they'd a learnt you, there, that people that acts as I'd been acting about that nigger goes to everlasting fire."
He blames the fact that he was brought up wicked.... irony can be found in the fact that Huck is doing everything he can to help Jim..... not to hurt him or turn him in.
Source(s): The Adventures of Huckleberry Finn