Again, both the things he did aren't wrong at all imo. Destruction of Ohara was indeed important from his perspective as they could've unleashed weapons that could potentially destroy the world. It was just cruel from our perspective because we felt for Robin. Also, executing Ace was nothing wrong as from his perspective, he was just a bad and powerful pirate. The only real 'bad' thing he did, in my opinion, was trying to kill Coby. However, I definitely don't want him to be redeemed at all because we're viewing the story from Luffy's perspective and it will definitely not feel right for his brother's killer to be redeemed like that. Though yes, I would like to have him be a grey character and not just pure evil (from our perspective) because of his Absolute Justice.