I think this is exactly what Benimaru warned Rimuru about, how killing humans could leave irreparable scars in his heart. Especially ones begging for their lives, or in this case, the lives of their children.
@kite722 Sure it may leave a scar in some, but what they beg for and Rimiru's purpose are two different things. Rimiru is no longer human, he knows from being on both sides regardless of world that there are good and evil people in all sentient lifeforms. All those participating had evil intent or a strong dislike of monsters. With Rimiru becoming a demon lord and all his subordinates getting and upgrade it ain't like many can take action against Rimiru and his friends. Just wondering how long after Veldora can be summoned or w.e
Just when I felt the slightest bit of sympathy for the invading humans, they had to go and say something really messed up. Continue the harvest, Rimuru.