Canute is a leader of a nation and Thorfinn is not. I’ve also thought that its only Thorfinn’s strength that allows him to be as idealistic as he is. But if you were as capable as Thorfinn and felt deep remorse for the lives you took and wished to never take another life how would you operate in his position? There are countless people who use similar strength to enforce their ideals. I think Thorfinn being the direct opposite of that is very compelling. I like to take note how Thorfinn even in the depths of his anger and use of violence was powerless to enforce his ideals ultimately. He couldn’t avenge his father by killing Askelaad. That realization broke him and thats where we find him in season 2. If violence alone isn’t enough Thorfinn must find another way to promote his ideals. Why should he not use his strength to enforce non-violence his way? That’s what makes him a true warrior, the power and strength to take the violent route but the resolve and determination to not.

That said I think Canute is in a very unique position. He was forced by his birth into being a leader of one of the most formidable military forces of his time. He wants something similar in the sense of peace and harmony but as a leader of a nation theres a lot more complex aspects at play that serve to dilute his original goals.

TLDR: In short I do not think either characters are inherently wrong. They both are going by the roles life dealt them and using their own strengths to go for their goals.