Most men who commit sexual offences have been "feeding on a diet of porn" first, Joy Te Wiata and Russell Smith say.
"Pornography is a no-no. It's like sugar to the developing mind, hard-wiring the brain."
They give the example of a 14-year-old entrenched in porn who started watching his stepmother in the shower, and went on to peep at windows.
The two are Korowai Tumanako, a sexual violence prevention and intervention service. In combination with Injury Prevention Aotearoa and Whanganui's Te Atawhai o Te Ao they gave a free workshop for Whanganui counsellors, social workers and community workers on Monday.
The 25 participants were very engaged and eager to learn more, Ms Te Wiata said.
She and Mr Smith have worked with perpetrators and victims in about 600 families. They define sexual violence as any harmful sexual behaviour, from rape to voyeurism, exhibitionism and derogatory sexual remarks.
"Before you can harm anyone, you have to first denigrate them."
Sometimes they work with perpetrators and victims together, which can be restorative. They've taken workshops about dating into high schools and dealt with famous people they are unable to name.
Sexual violence isn't a woman's issue, it's a men's issue, they say. From 85 to 95 per cent of victims are women - but it's women who have led the charge against it for decades.
Domestic violence has become something people will talk about, and men who are no longer violent can become its role models. Men who no longer perpetrate sexual violence can't do the same, Mr Smith said - emotions run too high about it.
A lot of men have difficult lives and use pornography, but it doesn't drive most to sexual violence. They have to choose it, and they also need an opportunity. Preventing sexual violence is possible. The two suggest:
-Reducing opportunities: For example, by teaching children to keep bathroom doors shut while they are showering.
-Pornography is a no-no: Keep young people's online activity in the open household, and monitor it.
-Make sure you know who is looking after your children: Even nice people can do harm, and harm is often done by people you know.
-Get police checks on people heading youth groups: Perpetrators seek out such opportunities. Even asking them about their tendencies can warn off potential perpetrators.
Perpetrators are not a lost cause. All but 5 per cent can change their ways. A five to 10-year community rehabilitation programme can reduce reoffending to 6 per cent.
Former perpetrators need to stick to a robust safety plan, and key people around them need to know about their previous activity.
Ms Te Wiata said it was great to see people change, and have successful, healthy relationships with consenting adults.