Can one be on the fence on this one? Like a good politician, I can see both sides of this issue.
Yes, by throwing the pearl into the ocean, Kino rids himself of all the things that come along with wealth...greed, selfishness, and the like. One has just to read the Biblical passage Matthew 19:24 (Again I tell you, it is easier for a camel to go through the eye of a needle than for a rich man to enter the kingdom of God.") to confirm the marriage of wealth and heavenly virtues.
Without money and status on which to rely, he then can return to his roots and focus on what is "important" in life...family...hard work...honesty...etc. In this way it is a victory.
However, as the previous poster said, since Kinoand his family have been doomed to live in the lower classes because of their life of poverty, losing the pearl represents a material and emotional loss. Without the wealth that the pearl brings, Kino cannot rise above his station in life to reach any dreams for his family.
Well, for purposes of discussion, I will take the other side of the question. There are strong political themes in The Pearl. In the novel, the Indian population is poor and powerless, viewed with contempt and preyed upon by the ruling class. Even the church is complicit, functioning as an extension of the establishment in exploiting the Indians. As a result, Kino is consigned to a life without opportunities. It has been ordained he will always be poor and powerless; it has been determined he will never rise above the social class and the social system into which he was born.
When Kino finds the pearl, however, he is suddenly filled with hope for a different future. He dreams of new clothes for himself and Juana, but his other dreams are more revealing of his deepest desires. He wants his and Juana's marriage blessed in the church, he wants a rifle (a means to hunt and to protect his family), and most significantly, he wants his son to learn how to read so that he will not go through life being cheated because of his ignorance. These dreams express Kino's desire to live as a man, not as the animal he is perceived to be by those who make up the power structure of his society.
Kino, however, does not stand a chance in realizing his dreams. The system is rigged, and the pearl buyers in the town conspire to cheat him. To sell his pearl for a fair price, Kino must leave his home to escape the forces that work together to hold him down. Before he can do that, he is attacked and tragedy ensues, one disaster after another.
When Kino returns the pearl to the sea, he does so in defeat. He dared to challenge society, to rise above his class, to gain a measure of power for himself, and to secure a future for his son. As a result, he lost everything he valued in his life, save Juana.
Definitely the return of the pearl to the sea from whence it emerged is a moral victory for Kino. You only have to read the novel to see how Kino changes under the malign influence of the pearl and to see that he loses more and more of his humanity as he fights to protect the pearl and the money and greed that it represents. Unfortunately, he needs to lose his son to be shocked back into his right mind. The relinquishing of the pearl comes after he has, in a sense, lost his soul, as he predicted he would if he lost the pearl, but he has done this only to find himself again and to return to being a wiser man.
In my opinion, his decision to throw the pearl into the ocean is a win-win for him and his family. The pearl is a symbol for materialism and wealth. It is an evil that corrupts and causes man to do things he would not do normally. By ridding himself and his family of this evil temptation, Kino is in fact, a savior. They are able to live simply and happily after it is absent from their lives. There is no anxiety about the pearl, what to do with it, how to spend the money it would bring, or worry about someone else stealing it from them. They are free to live simply with the carefree lifestyle they had before he came into possession of it.
As there is often some confusion by readers in interpreting Kino's words to his brother Juan Tomas, "If I give it [the pearl]up, I shall lose my soul," the evaluation of whether Kino's decision in The Pearl to return the pearl to the sea becomes equivocal. However, according to Elyse Lord, in an essay in Novels for Students, the meaning of soul is not the traditional definition. Instead, it signifies "human consciousness and potential"; that is his particular identity. Thus, when Kino throws the pearl away, he "undefines" himself, returning again to the natural order in which he has lived in "the blameless bosom of Nature in a quasi-animal existence."
Lord does, also, acknowledge that there are other interpretations to Kino's actions. But, taken with the idea of Steinbeck that people can only be fully human "once conscious of place with the entirety of creation," Kino throws the pearl back in the realization that this material object prevents him from living happily within what Steinbeck called "life's web." Juana, too, feels that they must be rid of the pearl which is "evil" so that they may return to the order of life which they have known. This feeling also coincides with that of Steinbeck who felt that salvation is only possible when the individual agrees to being part of a group; failing to do so leads to tragedy.