Most of us know about Black Beard, but the pirates with the really ruthless reputations tend to be the ones ignored in pop culture -because who want to idolize creepy, blood-thirsty monsters. For those of you interested in the dark side of history, you'll certainly enjoy this great Cracked article featuring the most terrifying pirates ever.
Link
BTW the story of Francois l'Olonnais eating a heart is almost certainly apocryphal. There are several reasons it may have come about
* There's the possibility that it was just a scary story made up by the Spaniards, the authorities still do that sort of thing today to make the bad guy seen even worse than he is.
* It may have just been popular myth. People like to tell a scary, grisly story. Look at contemporary tales of Jack the Ripper - many popular tales told of mutilations much worse than really happened. And people still do it today. Have you ever been in a bar in a neighbourhood where a murder has been committed. There's always somebody willing to swear that the murderer did all sorts of weird stuff that later turns out to be untrue.
* l'Olonnais may have made it up himself to further his own legend. The captain of an attacked ship will of course surrender more easilly if he thinks the attacking ship is captained by a heart eating psychopath.
* Or my personal favourite is that the surviving captives made up the story as an excuse for helping the bad guys. Remember l'Olonnais already had a history of freeing captives to send a message to his persuers.
One thing about the tale that really does make it doubtful is the fact that a man armed with a cutlass would find it fairly hard to hack open a man's ribcafe and removed the whole heart. More than likely he would make such a mess getting through the bone that there would just be a bloody pulpy mess in there and identifying any whole organ would be hard.