I was watching/reading Marineford for the umpteenth time and I kept noticing something.
There were multiple times in which Garp told everyone, Luffy included that he has to die before they can rescue Ace.
And it got me thinking.
Maybe Garp was looking for a way out. Making himself more of a target then necessary so he wouldn’t live through this, so he could die with the era, so he would die fighting like the soldier he is, so he didn’t have to feel guilty if Ace died and he was restricted from doing anything about it.
I mean Grap knows who Luffy will choose over him, it wouldn’t even be a question. Luffy does care about his grandfather, but they in no way share the bond the brothers have. And he makes an attempt to stay true to stay a loyal marine but knows it was futile, he couldn’t punch Luffy. Cause hitting Luffy would have stopped him and stopping him meant Ace died. So he was fully ready to take a possible fatal blow/fall for his grandsons.