When Rodion says he could be wrong, he means his words for the previous sentence:
> Hurrah for Sonia! What a mine they've dug there! And they're making the most of it! Yes, they are making the most of it! They've wept over it and grown used to it. Man grows used to everything, the scoundrel!
So he says that man must be a scoundrel to accept the fact that their own daughter works as a prostitute in order to support the family.
And if _that_ doesn't mean that man is the scoundrel, if _that_ is acceptable in the world of man, then there is no morality at all, and all the notions of good and bad are just superstitions produced by fear. And there are no barriers.
That's how I understand this passage.