Y'all acting like he's the devil and deserve internal hell for what he did but simping on other dads and MLs that did similar things. The only difference is this time the author choose to highlight what he did instead of passing it off like the other manhwas.. it concerns me how easily people are to be manipulated from only one highlighted point of view.
I'm taking a neutral stand so far. I can understand why Keira misunderstood the Duke's intention and why her heart is closed off. But I also can see why the Duke chose to follow traditions such as throwing his cubs off the cliff for them to be independent. It's how he was brought up. With the expectations and responsibilities carried on his shoulder.. you can also see that side of him is similar to Keira of the past: to follow the rules, to be the perfect Duke for the country, to produce the perfect offsprings as his heirs for peace and protect his family's honour. But like how Keira is, he is also awkward when showing affections because he was not taught how to. Because of this, Cosette had the advantage because she knows how to handle the Duke with her high social skills and with how she infiltrated family, Cosette most likely know the Duke's weakness too.
Also, based on his reaction to his dream, shows he still cares about Keira, his daughter. There could also be some triggers or curse that affected his mental health and made his head lose some screws in the previous life.
So I'm not saying he shouldn't be paid for what he did but I'm sure there's more to this story than what it seems.