Legalised "physician-assisted death" has not been used to kill people who may be "a burden to society", US research suggests.
Many fear a "slippery slope"
Some argue that allowing doctors to help people die could lead to the most vulnerable members of society being coerced into ending their lives.
The Journal of Medical Ethics reports no such evidence in Oregon, US, and the Netherlands which allow assisted dying.
The Pro-life Alliance still warned of the danger of a "slippery slope".
"Physician-assisted death" can mean either a form of suicide in which a doctor provides drugs in the knowledge that they will be used to end life, or active euthanasia where the doctor also helps administer those drugs.
The University of Utah study, led by Professor Margaret Battin, looked at hundreds of examples of "physician-assisted death" in both locations, looking closely at race, gender, age and medical history.
The average age of people choosing assisted suicide is 70, with most suffering from cancer.
There was no sign of any bias towards any other factor, including mental ill health or other chronic illness.
In Oregon, people without health insurance - in theory a far greater burden on their families - were not more likely to be helped to die.
The authors wrote: "We found no evidence to justify the grave and important concern often expressed about the potential for abuse."
They said that there were no facts to support the "so-called slippery slope" arguments about new assisted dying laws.
Ashley Riley, spokesman for UK-based campaign group Dignity in Dying, said: "This reaffirms what Dignity in Dying has always said - that medically-assisted dying can only act as a positive factor in patient choice at the end of life."
In the UK, a bill which would have made "physician-assisted suicide" legal was thrown out by the House of Lords in May 2006.
The debate over the issue was heightened by the case of Diane Pretty, a motor neurone disease patient who fought a legal campaign to make her husband safe from prosecution should he help her to die.
Anti-euthanasia campaigners say they fear that a change in the law might not only be abused but that it might lead to resources being diverted away from palliative care, the branch of medicine which aims to alleviate the suffering of terminally-ill patients.
A spokeswoman for the Pro-life Alliance said that other studies hinted that vulnerable people were at risk from assisted dying.
She said: "There was a 1995 study from the Netherlands which suggested that 900 people had undergone 'involuntary euthanasia'.
"As well as this, data from Oregon in 2005 showed that more than a third of the people who underwent assisted suicide said that one of their reasons for doing so was because they felt a burden to their families.
"I think the slippery slope is a real danger."
Peter Saunders, from the Care Not Killing Alliance, said: "If the law was changed in Britain, vulnerable people would feel under pressure, either real or imagined, to request early death whether they wanted it or not."