I don't know, I thought Dexter realizing he was too much of a danger to his son made a lot of sense, considering the fate that eventually befell everyone else
he came into contact with (Deb, Rita, Harry, LaGuerta, Doakes, etc). No matter how far away they ran, it was only a matter of time before Harrison became the next victim.
So I thought that made sense. The problem was just that the show just didn't earn that moment, or build up to it in a believable enough way.