I definitely think they have put the entire "dark passenger" idea up for debate with much of what has taken place this season and last. Dexter has been much more emotional as we have watched his relationships with Deb and Hannah. He has always showed basic parental emotions with Harrison, but if you think back to his relationship with Rita there was always this internal monologue that was debating how he act so that his emotions would appear genuine to those around him. With Deb and Hannah there has been much less inner debate and much more natural emotional reaction. Dr. Vogel has commented on it various times throughout the season.
For the most part the "dark passenger" has been presented as a uncontrollable impulse/desire/need that could be guided, but not stopped. However, there has been a lot of talk about Dexter's ability to choose this season and they have painted a potential future where he could be free of the grip the "dark passenger" has on him.