Loius Appreciation Post [it's a character analysis but shhhhh it's the same thing]
The interesting thing about Louis is that he is arguably the most innocent and violent among the Moriarty brothers. This man has committed the least amount of crimes compared to his brothers, yet he feels little regret when he does kill. The one thing that sets Louis apart from William and Albert is that he chooses to dip his hands in blood not only for the greater good, but also because he chooses his brothers above anything else.
I think if William and Albert were given the choice of creating a good world without killing people, they would do it. If anything, for the sake of their sanity. Their only motivation is the plan, nothing else. Louis on the other hand kills for love, he kills for his brothers. He kills because his William told him and he wanted to help out in any way he can. The only time I can think of when William breaks his rule of killing people for good is with Milverton, since he was a direct threat in the sense that the plan will fall apart if he finds out about William's real name. Even then, Milverton arguably deserved to be killed. Other than that? Nothing else.
Not only that, Albert and William are the only people that try to repent in self destructive ways. Albert isolates himself, while William tries to die, putting an end to the plan for good. But when that failed, he tries to find the answer to how to repent the right way.
Louis never repented like that. He must have felt grief and lose for William, but he never punished himself. He doesn't have that level of guilt compared to his brothers. He decided to serve his nation, helping out in any way he can. Just like when his brothers were around.
Louis loves his brothers a lot. He would do what they ask, even if it's not the morally right thing to do. He will spill blood of it means his brothers are content. And that's all he ever wanted. A calming life, helping people whenever he can and being satisfied with everything. Which is why he seems so innocent compared to his siblings.
If William and Albert are in the darker shades of grey on the morality spectrum, Louis is right in the middle. And he wouldn't have it any other way.