The family of the Marshall Ds are cowardly, double-faced people who will lie, cheat and steal to save their own hides. Don't you find it strange that the Ancient Kingdom, who was so florished and superior to everyone else in technology, lost to the 20 kingdoms? The family of Marshall Ds betrayed them.
Luffy and Teach are complete opposites(even their taste buds). The only thing they have in common are their charisma. Blackbeard is a real 'D.', but his cowardly nature and wiillingness to betray his own nakama is revolting to the other Ds. The 'Ds' chase after freedom.
Luffy and Roger wanted to be the freeset man in the sea
Garp remained a VA because it gave him more freedom to do what he wants
Dragon created the RA because he wants to free the world from the WG
Ace wanted the freedom to live his life his way so that he can figure out his self-worth
Saul defected from the marines because he believed the Ohara scholars were free to study and learn as they please
Joyboy wanted all life on the planet to be free and live together in harmony
Teach gave up his own freedom so that he could gain power(Yami fruit from WB's ship)