Mr Vickers, who is writing a book about his wife's dying quest, told the Herald that the criticism was unfortunate.
He was still deciding whether to attend the conference, but should he do so it would be "simply fallacious" to assume his attendance was an automatic endorsement of the views of organisers or attendees.
"I think in New Zealand we probably want more moderate laws, laws that are more similar to some of those in the US states, rather than some of the laws in the Netherlands and so on.
"I am interested in getting to the bottom of what is happening in the Benelux countries [Belgium, the Netherlands, and Luxembourg] -- understanding more about some of the assertions from people like the Care Alliance about just how unsafe they think that these laws would be.
"It is much an understanding thing, if I do decide to go, as it is talking about Lecretia's story."
Mr Vickers said recent attacks from the Care Alliance and its allies were "deeply undignified, insulting to Lecretia's memory, and unfortunately lowering the quality of the public debate".
"That they're resorting to such tactics indicates they must be losing faith in the quality of their arguments and their ability to debate fairly."
Mr Jansen said he was not attacking Mr Vickers personally, but publicising the fact he had been invited to the conference, and the views of conference organisers and some attendees.
"He has allowed his name to be associated with that [Euthanasia 2016]. I am pointing out the facts.
"[Assisted dying advocates] start with the thin end of the wedge, but I think people are entitled to understand what the thick end of the wedge looks like."
Seales was a Wellington lawyer who, dying of brain cancer, asked the High Court to give her the legal right for a doctor to help end her life.
On June 5, soon after being told that her court bid was unsuccessful, Seales died of her illness, at the age of 42. A judge ruled that only Parliament could make a law change allowing for that to happen.
In August, the Health select committee began the first parliamentary public inquiry into euthanasia as a direct result of Seales' court judgment.
In October, a bill legalising voluntary euthanasia was introduced to the ballot by Act leader David Seymour.
Mr Seymour has since turned down ministerial positions, saying he wanted to focus on championing that bill if it is drawn this year.
Twenty years of bills
1995: National MP Michael Laws' Death With Dignity Bill, jointly drafted with former MP Cam Campion, who was dying of cancer. It proposed that the bill would only become law after a binding referendum to be held with the 1996 general election. Failed to be referred to select committee by a vote of 61-29, with many abstentions.
2003: Peter Brown's Death With Dignity Bill narrowly failed to proceed to select committee stage.
2012: Labour MP Maryan Street sought to introduce a Member's Bill to Parliament (the End of Life Choice Bill), which would allow those terminally ill to choose when to die and to be able to receive medical support to do so under certain circumstances. She said it would only apply to people who were of sound mind and suffered from a terminal illness, or an irreversible condition that made their life unbearable, in their own view, and would need two doctors to attest these conditions applied and that the person had not been co-coerced.
September 2013: Street withdrew the Bill "because she didn't want it tainted by election-year dynamics". When she was not re-elected, Iain Lees-Galloway took up the Bill but in December 2014 it was formally dropped from the Private Member's Bill ballot at the request of new Labour party leader Andrew Little.
August 2015: The Health Select Committee began the first parliamentary public inquiry into euthanasia as a direct result of Seales' court judgment.
October 2015: A Bill legalising voluntary euthanasia was introduced to the ballot by Act leader David Seymour.
