He was not!!
He is seen in the most sympathetic light. He has a good heart educated by life experiences and a keen mind that knows when things are wrong. Of course that sets the two (Jim and Huck) to get into a discussion about what is in books.
Twain often uses Biblical Stories to illustrate the point he is trying to make. Chapter 14 in Huckleberry Finn is a classic example. Huck begins to tell Jim about Kings and Earls and Dukes and such and Jim is astonished. Then Jim makes the remark that sets up the moral point of Chapter 14.
Was King Solomon in the Bible Wise? Huck can relate the story. He has been well taught the "book leaned" version of Solomon. So it begins to tell Jim about splitting the "chile" in half.
Jim is horrified and angry. He points out to Huck in very a very straight forward manner that, that Solomon was not only not wise, he is without feeling and has no idea what the value of a child really is. Anyone with a good heart would realize that cutting a child in half is no solution at all. Jim goes on to say that he had thousands of children and one more or less made no difference to him. His heart, his humanity has been dulled by having too many of one thing that should be of immeasurable value. Jim knows something Solomon did not. Jim will do anything to get his family back.
Remember, you are reading a piece of literature where a different point is being made about the Bible than is usually told. Those are Twain's remarks, not necessarily anyone else's.
Not three chapters later we learn if Huck has heard him or not, and apparently Huck has.
I suggest you look at Chapter's 14 and 16 again. You will find out what all this means.
