MSPs have been urged to reject any future attempts to legalise euthanasia.
Mr MacDonald said fewer than 40% of doctors supported euthanasia
The Reverend Professor Donald MacDonald fears the care for people with terminal illnesses would suffer if assisted suicide was brought in.
Mr MacDonald from the Free Church College, who suffers from multiple sclerosis, has submitted a petition to the Scottish Parliament on the issue.
He told the Holyrood petitions committee that fewer than 40% of doctors supported assisted suicide.
A bill by Liberal Democrat MSP Jeremy Purvis fell last year after failing to attract enough support.
His Dying with Dignity Bill would have allowed capable adults with a terminal illness to access the means to die.
Mr MacDonald said he feared Mr Purvis or another MSP may make a second attempt to change the law.
In his petition he urged MSPs to oppose the introduction of such legislation.
He said: "I myself have an illness which is slowly deteriorating, multiple sclerosis.
"I may well have a slow, lingering death, but I don't want that process shortened in any way."
Mr MacDonald said he would want to ensure that all facilities, care and support was available to him.
"My fear is if such legislation comes in to legalise euthanasia or assisted suicide, people would rather take the easy way, people will lose the desire to give support and help," he said.
"For dying with dignity it is better to give all the support that is needed through palliative care rather than to just end a life by giving a lethal substance."
The churchman said assisted suicide went against the principle that the sanctity of human life should be upheld at all times.
He added it went against the Hippocratic tradition in medicine, that the duty of doctors was "always to care and not to kill".
"We should do all we can to relieve that suffering and give support to the very end," he said.
"It's wrong to put a burden on doctors and the medical profession to have a duty to end someone's life."
Committee convener Michael McMahon, who is also the chairman of the parliament's cross party group on palliative care, said the provision of palliative care with the development of facilities such as hospices for children should be built upon.
MSPs agreed to write to the Scottish Executive to ask their views on the issue, and also to contact the Scottish Partnership for Palliative Care.