How do Huck and Jim justify stealing?

From the text:

Mornings before daylight I slipped into cornfields and borrowed a watermelon, or a mushmelon, or a punkin, or some new corn, or things of that kind. Pap always said it warn't no harm to borrow things if you was meaning to pay them back some time; but the widow said it warn't anything but a soft name for stealing, and no decent body would do it. Jim said he reckoned the widow was partly right and pap was partly right; so the best way would be for us to pick out two or three things from the list and say we wouldn't borrow them any more—then he reckoned it wouldn't be no harm to borrow the others.