a parallel between Dexter and Kurt at the end
What spurs Harrison to kill Dexter is that Dexter killed Logan. A person who doesn't even come close to fitting the code. Only fits the "Don't get caught" bit, which at that point is really more delaying the inevitable. Basically just being in Dexter's way and showing his love of killing itself.
Could argue that Molly fits the same bill in regards to Chuck's motive and MO.