Yes, it seemed more like a knee-jerk reaction than something he'd thought through. I knew Deb was going to die from her wound, because Jennifer Carpenter let it slip in an interview she gave last week. But her death contributes to a loose string the finale left dangling. With both the Morgans gone, the police would surely have started looking for Harrison. They thought he would be leaving with Dexter, unaware that he'd already left with Hannah. Even if the cops didn't think of Harrison right away, Jamie (Batista's sister who took care of him) would start screaming "Where is he?" If they checked the airports, they'd find a boy Harrison's age had left with a woman who fit Hannah's description and they'd figure out what had happened. Argentina was undoubtedly chosen because it does not have an extradition treaty with the US, so Hannah is probably safe so long as she never leaves the country. Probably. But there was no time to crowd all that into a one-hour finale; what was needed was a quick and dramatic sacrifice to give us the final shot of the series -- Dexter miserable, alone, with only his martyrdom to keep him company.