@DSC:
Almost all tragic heroes are brought down because of their own flaws - for example, Hamlet. Ace isn't a poorly written character because he has character flaws.
However, Ace's flaws stemmed from his inability to forget the past and his inability to see any value in himself which caused him to justify his own existence though his service and relationships to other people. Not respecting a man he never met, whose legacy caused him great pain and is the root of his insecurites… that's not a flaw.
This is the truth of Ace's character and it was the way he was meant to be. The idea that he would make peace with his father is something that could give his character a completeness it was never meant to have. Had he lived Ace might have met Rayleigh after the war and made his peace with Roger, but to what ends? He's not the main character.
@DSC:
While Roger did give Ace to Garp, he didn't stick by Rouge when it's quite clear that his illness hadn't incapacitated him. Roger - rather selfishly - wanted to go down in a blaze of glory, on his own terms and that had grave repercussions for Ace's childhood. Why should Ace respect that when all he heard about his father was that he was vicious and cruel and that any child of Roger's deserved to die with him? Saying Ace should accept Roger as his father just because of the blood connection is silly and totally undermines the points Oda brought up with Whitebeard's character and his family of outcasts and also Sabo with his noble blood and status-obsessed parents.
On this point I think Aegir is right. Roger made the right decision under those circumstances. Since Roger has been described as anything but selfish I wonder why you assume his motives were. Staying with Rouge wouldn't have done her or Ace any good. Setting them up with Garp for protection was on point. Had Ace ever known the whole truth I doubt he would have had so many issues.