Dexter's father, who knew about his son's urges, taught him to use a "code" that would help him to control the urge and use it for good. Dexter's code is only to kill those people who are bad guys, or who have slipped through the cracks of the justice system somehow. What kinds of codes have we created for ourselves? "I'll only drink on the weekends. I'll only smoke when the kids aren't around. I'll only cheat when the spouse is out of town. I'll only get high when I'm stressed. I'll only eat until 7pm."
I've had a dark passenger. Several, actually, in the course of my lifetime. Some I'll freely admit to, some I won't. I suspect I'm not alone in this. Anyone who has ever dealt with an addiction understands the concept of something other than ourselves calling the shots. I think that's why shows like Dexter thrive. People identify with a character who seems to have come to term with his urges, whether he's controlling them, or they're controlling him.
As Dexter learns his dark passenger is not a separate entity, but a part of himself, we can learn the same lessons. How much more at peace would we be if we could accept ourselves completely and as one integrated human being? Flaws and all. Sometimes merely embracing those flaws and admitting them gives us the strength and courage to change the behavior or take the power away from the dark passenger.
If things feel out of control and you think you need help, ask yourself who's in control of your life? You or your dark passenger? Even if it is your dark passenger, you are not alone.
If you're struggling with an addiction or causing harm to yourself or others, I urge you to seek the appropriate help. Dexter may be a fascinating television show, but it's no way to live.