Clan member. Namely, at multiple points in the series, including when he begged for his life from the former Emperor Whitebeard on Marineford, Blackbeard has shown a notable lack of this quality.

Clearly, Oda would have had Blackbeard steal Whitebeard's devil fruit in Marineford anyway. This would mean that Ace would have had a grudge against Blackbeard, but he wouldn't have thrown his ...