Are You...? - S7-E1
Continuity mistake: When Dexter started removing the plastic off Travis' body, his small knife was stabbed into the chest, but during that, the sword was already stabbed into the chest, not the knife, and then again, he removed the knife from the body, and then stabbed him with the sword. (00:12:05)
Are You...? - S7-E1
Plot hole: It's out of character and against his code for Dexter to kill Viktor at the airport. Airports have security cameras everywhere (you can see one on the ceiling when he is wheeling Viktor into the unclaimed baggage storage), and using the unclaimed baggage storage as the kill room is equally unwise, because any airport employee could walk in at anytime and catch him red-handed. Dexter was caught murdering Travis Marshall by Deb just hours before, so if anything, he should be even more cautious.
Are You...? - S7-E1
Factual error: During the walk-through of the crime scene, there is a small remnant of plastic sheeting between Travis' toes. Given the entire church was consumed by flames, or more importantly, the body and foot from which the plastic is pulled are badly burnt, it's highly improbable that the plastic sheeting would still be present. At least not in the form that is shown, but rather more like a globe of melted plastic on or into the body or table. Similarly, the feet wouldn't be 'wet' or glossy with blood. (00:15:22)
Answer: Two reasons. First, as a cop he knows that there are lots of murderers walking around free due to flaws in the system so he uses Dexter's "urges" to right the wrongs in the system by taking out people who have no right to walk around free. Secondly, by taking him to a psychologist he runs the risk of having him committed and he doesn't want that for obvious reasons, so he figures it is best to channel his urges to what he considers a greater good.
The_Iceman
In addition to the earlier answer, in the last season (8th) of the show, we are introduced to Dr. Vogel, whom Harry had been discussing the situation with Dexter as well, and it is shown on-camera that Harry describes what Dexter has done (killing)... So, technically he did consult a psychologist/psychiatrist, just not having Dexter and her actually meet. But Dr. Vogel was aware of whom it was and how to intercede.