Propaganda and lies. Each chapter I'm mpre convinced that the true first rebel was Rocks and what we see in God's Valley, including his end, will inspire Dragon to rebel directly and Roger to do it indirectly.
Roger became the pirate king for the masses to hide Rocks from history but he also inherited his will. I'm convinced that's why Roger seems like such a goof in this flashback, he just wanted to fuck around with his fruends, God Valley and Rocks gave him something to dedicate his life (and death) towards.
Also, seems like Morgans wasn't part of Roger's crew, sad, I liked that theory.