@Impel:
Who says Dragon loves Ace? Who even says Dragon is his first-born?
Dragon is Ace's firstborn now??
@VL7:
Ace is his son(as long as it isn't stated otherwise in the manga or from Oda personally). I think he shold get at least a little bit emotional before starting to get tactical. Though the Ds don't seem like very good parents anyway…
Maybe not, considering Garp's son went on to become the World's Most Wanted, and Luffy never knew his father.
And I don't even wanna think about Teach having children.
But remember the way Saul acted towards Robin? That guy would've been a great father. And maybe Dragon abandoned his children so they wouldn't be the sons of a criminal (cue Nico Olivia).
And after all, Garp did come back for the offspring of his wayward son… although he did try to kill one of them.
We gotta think here, though. Blackbeard kills Ace. Who is going to get pissed?
Dragon.
Luffy.
Whitebeard's entire crew.
Possibly Shanks.
Blackbeard has just made himself Public Enemy #1.