Ever since he was young, he strongly stuck to what he believed it and worked towards his goals. When Titans were the enemy, he focused on that, going as far as saying he would eradicate every single one of them. But once they got rid of that threat and realized Marley was the true enemy, I'm assuming his goal is now to destroy that country entirely. Have them feel the pain his mother felt or the despair his father went through. Not just them but everyone on Paradis Island. He's out for blood and everyone he considers an enemy is gonna get wrecked.
I'd actually liken him to Daenerys in Game of Thrones lol. While her enemies were the slave traders and Cersei's army (monsters), everyone supported her. But once she shifted her target to surrendered soldiers and "innocent" citizens, she became the monster in their eyes, when to her they were all just enemies to be eliminated.