Not that the son is much better than the father, but it seems as though you already destroyed the root of the issue by killing his father, given that he was the one who implemented the exploitation of your Mother.

I could hardly argue that he's deserving of any particular mercy, or that he isn't a conniving little snake in his own right, but I'm not certain of the validity of his inheriting the sins of his father. It's not as though you need the excuse that he was somehow involved with hurting your mother to make him contemptible.