Why does Stevenson make such an effort to show Long John Silver's positive traits?

Throughout the novel, Long John Silver clearly possesses a dual personality (thus, many critics also view Long John Silver as a precursor to Dr. Jekyll and Mr. Hyde). It is thought that Silver combines two pirate characters that appear before Silver makes his appearance in this novel. First is Billy Bones, the blustering buccaneer who is basically good hearted and kind to Jim, and the blind beggar Pew, a deformed, apparently harmless but who is in fact very strong and extremely cool. At times, Silver shows extreme kindness and a paternal liking for the young narrator. At other times, however, Silver, although deformed like Pew, shows extreme brutality and cruelness in killing other sailors.

Robert Louis Stevenson paints this character much more vividly than any of the "good" or "bad" characters and Long John Silver is not "good" or "bad" but rather a composite of both. Because of his openness about his greediness and mercileness, his pursuit of the gold seems more justified than the greediness and evilness of the "good" characters. This character is based on the Stevenson's friend, the poet W.E. Henly, who lost one of his feet. Of all the characters painted in Treasure Island, Long John Silver is the most vivid, most remembered, and most picturesque.

Long John Silver may be the pirate's captain but he has a good heart. He takes up a liking for Jim and strikes a bargain with him. He tells Jim that if he saves Jim from thepirates he will be a witness when they go back to bristol. Jim agrees to this conditon. He soon relises that Long John is a good person and the pirates are making a mistake by dismissing him as captain.