Pandering to rightwingers' fantasies about gunning down the evil people (even if they're careful to integrate the ethnicities of the righteously slain villains,) counts as edgy?
Dexter's kills are the least interesting thing about Dexter. And his success is targeting killers and getting away with it demands increasingly ridiculous plotting.
Of course, broadcast tv is incredibly conservative. That said, starring Lawrence Fishburne on CSI is much edgier. Giving a show an atheist hero is much edgier. (Never thinking about church or praying isn't atheism, it's the norm.)