I wouldn't say they were all really unpleasant people. I think a lot of pop culture and propaganda of the time tries to portray them as blood thirsty, dangerous, and murderous villains. Some were painted as pirates when they were merely trying to aid their country. Take, for example, Francis Drake, who raided and pirated ships of the Spanish Navy to aid in the cause of England, was painted as a pirate and monster by the Spanish.
A lot, from my understanding, were just looking to make a better life not only for themselves, but for their crew members as well as their families. From my own understanding, they did not purposefully seek out the act of murdering crew members of ships. They were often given a chance to be assimilated into the pirating crew, or stay on the disabled and pillaged ship. It was the goal of being their own man (or in some cases, women) that didn't bow to a King or Queen, or worked and gave their hard earned pay for the taxes and rich. Their priority, in my readings, was a desire to gain wealth and make a better lives for themselves.
Pirates were among the first, in my opinion, to bring a sense of Democracy into the New World. Captains and Quartermasters were elected by the crew, with a checks and balances system in place as well as every equal shares (with some raises in injury pay) for raided ships.
In a group game that I'm currently co-GMing (shameless plug), I have two pirate captains of their own different ships. One is a ship made up of freed/liberated slaves, and the other is just a ship of sailors. Their endgame, their main driving purpose, is the betterment of their lives. I can't speak for the others who are writing pirate captains (I do know that some are writing slavers), but I think, in the end, at least for my characters, it's about making a better lives not only for themselves, but of their crew mates as well as their families as well.
A really good book that I would really recommend for people wanting to learn more about the Golden Age of Piracy is "Under the Black Flag" by David Cordingly