According to Robert Louis Stevenson, pirating isn't just a job, it's a way of life. By which we mean that all the pirates in this book seem to have basically the same characteristics. Sure, on a scale from pathetic weakling (Ben Gunn) to awesome genius (Long John Silver), they all check in as more or less courageous and more or less competent. But despite these individual variations, all pirates basically have three traits in common:
We find it hard to believe how much rum is consumed in this novel. But the rum is really a symptom for a more profound problem, which is that pirates have no discipline. After all, discipline belongs to hierarchical, orderly systems like the navy, which pirate society is all about fighting against. Still, this lack of discipline is also the main thing that keeps getting in the way of the pirates' success.
After all, they elect Long John Silver as captain when things are good, but as soon as they turn bad, it's every man for himself. Once they gain control of the fort on Treasure Island, they utterly fail to set a guard, allowing Jim Hawkins to walk right smack into the middle of them without anyone knowing. Of course, Jim is as surprised as the pirates are by what he has done. Even so, he takes the time to notice that, "there was no doubt of one thing; they kept an infamous bad watch" (27.24). And this lack of discipline has much more dire consequences for the few remaining pirates when it allows Doctor Livesey and Ben Gunn to get the drop on them in Chapter 33. The flip side of the glamorous, carefree life of the pirate is that these guys have no sense of self-preservation or self-control, which winds up getting most of them dead.
Ben Gunn takes advantage of this trait to freak out George Merry and Tom Morgan on their final treasure hunt. He very nearly convinces these two hardened pirates to give up the quest they have spent so much time and energy pursuing just by imitating the last words of Captain Flint in a ghostly voice. Even Long John Silver, who seems to be made of iron, is unnerved by this performance. Or take Dick Johnson, who becomes so convinced that he is cursed after cutting a piece of paper out of his Bible that he immediately falls into hallucinations and fever.
This superstition that all pirates, even super pirates like Long John Silver, seem to share appears to be the result of their life of crime. After all, as Jim comments about Long John Silver at the end of the novel, "It is to be hoped [that he is living in comfort with his wife and parrot], I suppose, for his chances of comfort in another world are very small" (34.25). In other words, pirates are criminals, so they won't be going to heaven. And this Christian world that they all seem to come from (Ben Gunn claims to have been raised religiously and Dick Johnson obviously carries a Bible with him) gives all these pirates an intense fear of death. They may be living hard and enjoying themselves, but they all seem to fear what their eternal punishment will be.
When Black Dog manages to track down Billy Bones at the Admiral Benbow Inn, what happens? Billy chases Black Dog, bleeding, out of the building with his sword drawn. When Long John Silver fails to talk loyal Tom (not Tom Redruth; some other, random Tom) around to the pirate cause, what does he do? He hits the guy with a branch when Tom's back is turned then shoots him twice. Israel Hands and O'Brien are so intent on killing each other aboard the Hispaniola that they don't even notice Jim has cut the cable fastening the Hispaniola to its anchor. And Captain Flint (the pirate, not the parrot) is famous for murdering six of his own crew while ashore to bury his treasure.
What does all this violence prove? No matter how well-spoken and gentlemanly a pirate may appear, the pirate code is pretty much every man for himself. Since these guys all live outside of established social codes and relations, no pirate seems to feel too much obligation to look out for anyone else. The only thing that keeps these pirates in line is mutual suspicion and the constant threat of violence.
Because there's no set hierarchy or government in pirate society, they seem to work according to oddly democratic principles. They elect the man they most respect (in this case, Long John Silver) to be captain. At the same time, without the rule of law, these elected captains aren't protected from the quarrelsome violence of their men. Take a look at poor Long John Silver by the end of the book: he almost gets killed by the people who elected him just a few days before! The pirates pretend to have rules and regulations, with their demands to right of council and their black spots (about which, see "Symbolism, Imagery, Allegory"). But it really all seems to boil down to who's the strongest man at any given time. Might definitely makes right among pirates.