Chapter 3 of John Steinbeck'sThe Pearlholds the answer to your question. In this chapter, Kino's great luck at finding "The Pearl of the World" is slowly beginning to turn into a burden. For once, everybody has already been made aware of the existence of this pearl. Moreover, this legendary pearl has been the goal and dream of many pearlers and fishermen just like Kino. Hence, Kino is now looked at as the enemy for, in the men's minds, Kino has come in between them and their dream of the pearl.
Considering Steinbeck's style and purpose as an author, it is not likely that he would bypass treating the real themes of this novel such as human nature, ruin by greed, social injustice, and classicism, just to bestow all the weight of the plot upon an inanimate object, such as is the pearl. Instead, Steinbeck is clear it is the pearl which has become stained by human contact, for humans are not appreciating it for the rare gift of nature that it is. Instead, all that the men see in this beautiful, unique, and rare event is money, material things, and greed. This accountability of human action and thought in the face of desolation is more like Steinbeck's style of writing.
Kino had found the Pearl of the World. The essence of pearl mixed with essence of men and a curious
dark residue was precipitated. Every man suddenly became related to Kino's pearl, and Kino's pearl went into the dreams, the speculations, the schemes, the plans, the futures, the wishes, ...of everyone, and only one person stood in the way and that was Kino, so that he became curiously every man's enemy
Therefore, the pearl is not what makes them evil. It is human nature what makes them evil. Sometimes it may even be their anger and frustration at the injustice of the world what made them act, or think, in evil ways. The peal is merely the conduit of all those human emotions, and the sum of every dream of those desperate men. This is why it ended up causing more havoc than good and, in the end, Steinbeck made sure to return it to where it came from.