Do You See What I See? - S7-E11
Continuity mistake: Deb's daily drive is an E46 '03-'06 BMW 3 series. In this episode she is in a car accident and when Dexter shows up at the salvage yard to check the vehicle he is led to an E36 '95-'99 3 series. (00:18:45 - 00:36:25)
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)
Factual error: In The Beginning while Dexter is on his boat in Miami, you suddenly see mountains in the background, of which there are none in Miami. Also the palms are too high, indicating they are from California. And the worst setting mistake is the Florida tags in front of the cars. Only commercial vehicles have front tags.
Sunshine and Frosty Swirl - S7-E2
Continuity mistake: When Wayne Randall is eating ice cream, the size/amount of ice cream on the cone changes as the camera pans back and forth between characters.
Continuity mistake: Near the beginning of episode 3, season 7, Dexter is attempting to take a mouth swab of a criminal in the interview room. When he first sits to request a swab from the man he is shown putting on forensic gloves. When the camera pans to him a second time to attempt taking a swab he no longer has forensic gloves on. As the man resists opening his mouth for a swab check Dexter is wearing forensics gloves again.
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)
Continuity mistake: When Hannah calls Dexter at the bus crime scene, Dexter answers the phone normally but then in the next cut, the phone is upside down. (00:23:25)
Sunshine and Frosty Swirl - S7-E2
Revealing mistake: After Isaak Sirko killed Tony Rush by sticking a screwdriver in his eye, Rush almost instantly drops dead on the floor. When Sirko's assistant, Jurg, wipes the screw driver for finger prints, you can still see a pulse at the base of Tony's throat. (00:54:05)
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.