"I'm going to ask you to put to one side any views you might have about whether it was morally appropriate a middle-aged man sought the company of younger people, of whatever gender, in the way he did," he said.
He questioned the attempt by the defence to "take the moral high ground" and reminded the jury: "This is not a court of morality".
What was important, Mr Johnstone said, was the dispute over what happened in the motel room.
In the witness box, Nattrass-Berquist said the victim sexually assaulted him, placing one hand around his throat and the other on his groin.
The teen said the attack only ceased when Wallace-Loretz returned to the room and came to his defence, using a bottle as a weapon.
But Mr Johnstone said there was no evidence to corroborate that account.
"What is it that makes a gay man more likely to be physically violent than a straight man?" he said.
"Nothing. An apparent preparedness to pay for sex tends to suggest a disinclination for violence."
Mr Johnstone also pointed to the injuries sustained by Mr Gillman-Harris, which he said were inconsistent with the defendant's version of events.
A pathologist found up to five injuries causing fractures to the victim's skull, as well as a 27cm bruise to the abdomen.
The lawyer said - rather than a bottle - the injuries were caused by a bat, which was taken to the venue specifically for that purpose.
He showed jurors CCTV from outside the motel and drew their attention to a "rigid object" that Wallace-Loretz had allegedly attempted to conceal.
Mr Johnstone also highlighted the text messages between the defendants, which he said showed them discussing a proposed violent robbery.
"These two defendants just happened to have done exactly what they appear to have planned. It's not a coincidence Mr Gillman-Harris was beaten and robbed; it was what these two planned to do."
Nattrass-Berquist explained the text messages as youthful bravado but Mr Johnstone rejected that.
Both defence lawyers are expected to close their respective cases this afternoon.
THE CROWN'S "FIVE PLANKS" OF ITS CASE
1. Injuries - The injuries to the victim were inconsistent with the way the fight was described by Nattrass-Berquist. The teen's story does not account for the five severe blows to the man's head.
2. A Bat - The defendants claim they used a bottle in the beating of Mr Gillman-Harris but Mr Johnstone said they had access to a bat that had been stashed in a Pakuranga car park. "The fact a weapon of that nature might have been used speaks volumes of the plan to rob," he said.
3. Text messages - The communications between the pair shows the developing of a plan to beat and rob the victim. The plan was "grounded in reality", the Crown said, rather than a display of adolescent bravado.
4. Stolen property - The teens allegedly took cash, a credit card, an iphone and the victim's car. Mr Johnstone questioned why they would have done that if they beat the victim out of self-defence and feared for their safety.
5. Behaviour afterwards - They looked to see the coast was clear as they took the victim's Range Rover. "Why didn't he call police? Why did he feel he needed to take the car to get away? Or at least, why didn't he call an ambulance," Mr Johnstone said. If they were innocent, why did they attempt to avoid detection?
