Mental Health Foundation chief executive Shaun Robinson says National's use of mental health claims around Andrew Falloon "very much smacked" of an effort to deflect from bad behaviour or poor political choices.
There has been a public outcry over the use of mental health as an excuse for the behaviour of the former National MP, who has retired immediately after it was revealed he apparently sent an indecent image - not of himself - to a 19-year-old woman.
Since then, other women have come forward with similar claims against him.
His initial public statement cited unresolved grief related to the recent suicide of a friend.
At the time, party leader Judith Collins said Falloon was suffering from significant mental health issues and called for the public to respect his privacy.
Mental Health Foundation chief executive Shaun Robinson today told Morning Report it appeared Falloon had used mental health concerns as a shield.
"First of all we have to acknowledge the mental health and wellbeing of the women who were victims of his actions. Their mental health, the support they are receiving, the impact of his actions on them I think should be the paramount concern of everybody.
"We need to make a distinction between people's mental distress and their actions. When people are experiencing mental distress they do need support, they do need our compassion but that does not excuse people for their actions at that time
"There seemed to be a very strong implication that that's what the initial response to Mr Falloon's mental state and his actions was trying to do."
Robinson agreed Falloon's actions were not the symptom of any known mental illness, but said that was not the point.
"People can be mentally distressed because of things that occur in their lives and in fact we need to be careful not to confine our definition of mental health to a clinical model of mental illness ... I live with bipolar disorder [and] I would actually be furious if people used that as a kind of way to judge my actions at a lower standard of ethics and responsibility because that is another form of stigma and discrimination.
"It's saying if you are experiencing mental health challenges ... we can't really expect you to be a fully functioning human being."
"I can't really speak to the motives of the National Party ... but the public are not stupid and they can see when people are not being authentic and are using the very strong concern of the New Zealand public around mental health as a kind of a buzzword to deflect attention away from bad behaviour or poor political decision making and I think this very much smacked of that."
Asked if using mental health as an excuse in this kind of situation was demeaning for others who were living with mental health conditions, Robinson said: "Totally. It's totally demeaning. It's not taking the experience of mental distress seriously."
It put those people into a category of "other" who would not be judged by the same standards of humanity as everybody else, he said.
Collins told Morning Report that National had not used mental health as a smokescreen.
When Falloon first spoke to her about the issue, she was "very confident that when he told me he had a significant mental health issue ... that I was dealing with someone who was clearly not well in some form.
"In fact ... when I talked to him I was very concerned that we got him home safely. One of my big concerns was that we would have a suicide."
She arranged for him to be flown home with people to support him nearby, she said.
"Yesterday it was confirmed early that he had the right people with him in terms of mental health.
"I was assured that he had the right level of assistance and look, with what he has done - which is absolutely despicable - he is still a human being and we have to remember that his family did not know about what had been happening ... and he had been extremely secretive."
Asked if she was confident that all scandal or dirty laundry was out of the National Party, Collins said: "I certainly hope so.
"I told the caucus yesterday very plainly that anything that people feel might be a problem they need to come and see me or the whips or the chief of staff, that where we can we will always assist our people, because people make mistakes and I'm not going to tell them they can't be mistakes because they make mistakes."