The claims will be discussed in Edinburgh this week at what is billed as the first gathering in Europe of campaigners against assisted suicide.
Care Not Killing – an alliance largely of religious groups – has been accused of "cheapening" the issue by opening its conference, the European Symposium on euthanasia and assisted suicide, with a talk entitled Lessons from Nazism.
Dr Andrew Fergusson, a former GP who is chairman of the advisory group for Care Not Killing, admitted the opening theme of the event would be "controversial". He said the comparison stemmed from a judgment in the Nuremberg Trials which said Nazi doctors believed in the existence of a "life unworthy to be lived".
The organisers of the conference have described the event as a "rallying of the troops" ahead of "major battles" in 2013.
Parkinson's sufferer Margo MacDonald MSP denounced Care Not Killing for drawing parallels with Nazism. She is to make a fresh attempt to introduce legislation to permit assisted suicide in Scotland – the details of which will be unveiled in the next few weeks – after a previous attempt failed.
Last night, Tony Nicklinson's widow, Jane, also attacked Care Not Killing. Nicklinson, 58, a victim of "locked-in" syndrome, came to public attention when he lost a legal bid for doctors to end his life. He died from pneumonia two weeks ago after refusing food and fluids following his failed High Court case.
Jane Nicklinson said of Care Not Killing's agenda: "I think it is totally ridiculous and total nonsense. How you can compare [the right to die campaign] to a Nazi death camp I will never know.
"It is scaremongering, pure and simple – half the things they say are nonsense. They will say something like that and then people who don't know much about it will think, 'We can't have that'. It is irresponsible – they are not giving people the true facts."
Around 75 people from countries including Canada, the US, Australia and the Netherlands are expected at the European Symposium on euthanasia and assisted suicide which runs from Thursday to Saturday in Edinburgh.
Explaining why the Nazi parallel had been drawn, Care Not Killing's Fergusson said: "Kids in schools in Germany in the 1930s were doing sums about what it cost to keep a mental defective alive and how many textbooks you could buy for healthy, blonde-haired, blue-eyed Aryan children for that money. It was that whole idea of some lives aren't equal to others and we stand against that."
Fergusson was keen to point out he was not suggesting those in Scotland in favour of euthanasia are Nazis.
He said: "We are not going to dwell on it [at the conference] – it really winds up the other side if they sort of hear the echo of the jackboot in what we are saying.
"I know that so-called right-to-die societies will protest it is not about a life unworthy to be lived, it is about personal choice – that is the philosophical debate between us."
Polls in the UK have suggested 80% support introduction of right-to-die legislation. But Fergusson says "biased media reporting focused on tragedy" has influenced these results.
He said the conference aimed to share information and "rally the troops" amid the two consultations on bills from MacDonald and in England from Lord Falconer, and the outrage prompted by the Nicklinson case.
"I think we can confidently say nothing is going to happen before the end of 2012 significantly, but we are gearing up for some big battles in 2013," he added.
Yesterday Independent MSP MacDonald accused Care Not Killing of "cheapening" the issue: "This is improper behaviour on their part," she said. "If they want to have a conference on Nazism and particular aspects of that creed, then I suggest to them that they separate it from a conference about assisted dying, because the two have nothing in common. They have cheapened their campaign."
MACDONALD'S previous End of Life Assistance Bill – which would have let people with progressive degenerative conditions as well terminal illness seek a doctor's help to die – was rejected by MSPs in 2010, by 85 votes against 16.
She launched a fresh consultation on the issue in January, aimed at clarifying how much a doctor could help a patient.
The results of this are expected to be published in two to three weeks. MacDonald will then need signatures from 18 MSPs to take a private member's bill forward in the Scottish Parliament.
She said she was confident it would win support and believes it could be introduced before Christmas.
"It is such an important bill and it has become more important as I think there is a greater chance of it passing," she said. "Therefore it's very important it is a good, robust bill and it's well drafted, so we are not rushing at it."
Meanwhile, Labour peer Lord Falconer has committed to tabling assisted dying legislation as a private member's bill in the House of Lords next year. Last year he headed a year-long commission into the issue, which concluded a choice to end their own lives could be safely offered to some people with terminal illnesses, if stringent safeguards were observed.
A consultation on Falconer's draft Assisted Dying Bill launched by the all-party parliamentary group on choice at the end of life, and pro-assisted suicide group Dignity in Dying, is currently being carried out.
Conservative MSP Mary Scanlon was among those who voted against MacDonald's bill two years ago. She said she had been concerned the legislation was not robust enough, for example in protecting elderly people from being pressured by relatives into ending their lives.
She said: "I would be coming to the new bill looking for my concerns to be addressed and I have an open mind on it. I am not totally against it – with the Tony Nicklinson case, nobody could fail to be moved by his request.
"The Conservatives have got an absolutely free vote on this issue. I know some of my colleagues are in favour, some are vehemently against.
"If I am given the assurance as much as possible that it cannot be abused then I may consider voting for it."
Labour MSP Michael McMahon, convener of the Parliament's cross-party group on palliative care, also voted against the bill in 2010, but said he would not change his stance.
He argued there was still a long way to go in developing care and pain relief for dying patients and introducing assisted suicide would halt this progress.
"It has an impact on the medical professions, it has an impact on families, it has an impact on the relationship between GPs and other patients," he said. "There are real concerns about the unknowns in terms of the relationship between the public and the medical profession."
The political landscape has changed significantly since the introduction of MacDonald's last bill, with 46 new MSPs after the Holyrood election.
Some representatives of the medical profession are also opposed to the introduction of assisted suicide legislation.
In a response to MacDonald's consultation, GPs' group BMA Scotland said it was concerned it "could alter the ethos within which medical care is provided".
The Church of Scotland and Catholic Church are vociferously opposed to the legislation. And disability group Scope has expressed concerns over assumptions that disabled people's lives "aren't worth living".
Its chief executive, Richard Hawkes, said: "The current law is designed to protect disabled people against these assumptions leading to anything worse – such as pressure to commit suicide.
"Many disabled people tell us that even though they might consider, in extreme circumstances, ending their lives, this is outweighed by a real concern about the consequences of any weakening of these safeguards. These concerns can get lost amid the din of high-profile advocates of legalising assisted suicide."
Raymond Tallis, former professor of geriatric medicine at the University of Manchester and chairman of the group Healthcare Professionals for Assisted Dying, turned angrily on Care Not Killing for making comparisons with Nazism.
"The idea that lining up thousands of people to shoot them is the same thing as acceding to someone's settled wish to die when they are terminally ill and mentally competent indicates how morally blunting it can be when you have religious beliefs."
DR Libby Wilson, medical adviser to the Scottish right-to-die support group Friends at the End, said: "It is incredible that in 2012 we are still debating whether people can be allowed to end their suffering if they feel it is intolerable. To me it is exactly like looking back on the middle of the last century when consenting sex between adults of the same sex was a crime and when abortion was illegal.
"Most of the opposition comes from people who are faith-based. They are perfectly entitled to their own views, but why should their beliefs govern what other people who don't have the same beliefs do?"
Dignity in Dying chairman Sir Graeme Catto, emeritus professor of medicine at Aberdeen University and a former president of the General Medical Council, believes legislation will come.
"It is one of the last major liberal policies and it is going to come in, because the public want it and in a sense need it," he said. "Why should they not have a choice at the end of life?"
He added: "Nazis didn't actually ask the victims if they wanted to be put into gas chambers or euthanased. Our view is that this is led by the individual – the individual asks for this, not the state or anybody else."
EXCLUSIVE BY JUDITH DUFFY