Emotionally, Sengoku truly did not want to see his old comrade's only grandson end up in such a situation.
All along, as Fleet Admiral of the Marines, Sengoku had actually shown Luffy considerable leniency. If not for that leniency, from the moment Luffy slipped out of the Marines' sight, he could have dispatched powerful fighters to bring Luffy back.
However, Sengoku had also considered that a child Luffy's age would be stifled if he were "confined" to headquarters all day, attending classes and training. When Luffy ran away, Sengoku had softened his heart and wanted to give him some room to breathe.
He had hoped that after Luffy truly witnessed the cruelty of the sea, he would return to Marine Headquarters.
And after leaving Marine Headquarters, Luffy had not actually committed any major violations of principle, which put Sengoku even more at ease—until Luffy caused a huge disaster on Fish-Man Island.
He injured the New Marines' island garrison commander and indirectly caused the bloodshed on Fish-Man Island.
Although the true culprit had been the Celestial Dragons, the lawless nature buried deep in Luffy's bones had already begun to show itself on Fish-Man Island.
At that stage, if Sengoku had been tougher and directly sent powerful fighters to forcibly bring Luffy back to Marine Headquarters, there would still have been room to turn things around. But the series of events that followed left Sengoku with no way to spare attention for Luffy's affairs.
And once Luffy entered the New World, he was like a dragon returning to the sea, finally letting himself loose completely.
Luffy's heart was kind, but his personality was also stubborn. Anything he set his mind on, he would accomplish by any means necessary.
Personal emotions completely governed all of Luffy's actions.
Yet a normal person's actions absolutely