Just having watched the 3rd season on DVD, I suddenly realized that the guy who plays Dexter Morgan is... gulp, a ginger.
A soulless ginger! How appropriate. Another name for Dexter might be He-Who-Is-Empty-Inside. He says so repeatedly, and this is the premise of the whole series, that this is about a guy who (because of witnessing his mother's chainsaw murder and being locked in a storage container with pools of blood from same, for a couple of days before police found him) is completely lacking in empathy, does not really "feel" emotions and has spent his entire life studying, imitating & acting the necessary emotions everyone seems to expect to see in you.

I like the show because there are so many innocent and good characters in it. They spent the 3rd season showcasing everyone's vulnerability, and maybe that's why it appealed to me even more than the first 2 seasons. Vulnerability makes a person seem innocent. Or at least it opens a door to empathizing with the character. It's interesting and ironic that the writers are working so hard on making you empathize with everybody.
I started thinking about this after reading the financial news, and wishing more models of ethical behavior could be found in art, fiction, TV, movies. While this show is darkly humorous because it's about a killer, it actually bothers to examine things like honesty and compassion.