Roger and his successor Luffy are the bright side of the coin, they don't wamt to rule the world but have an adventure, have fun (same as Shanks, WB falls here too, he jist wamted a family). While Xebec and his successor BB are the darkside, so much that Xebec didn't even stop at pirate king, he wanted to be the king of the world. This pretty much is the difference, Luffy, and so Roger and his will, are the good guys (even if it seems Roger at the very least slaughtered Sguardo crew but Luffy is clean) while BB, and Xebec whose will he inherited, are the bad guys and if they win the world will fall in chaos and darkness (litterally). And here, inherited will or not, you get the usual shounen troupe where there are the good vs bad guys.