Allowing doctors to assist terminally ill patients to commit suicide would "contaminate the medical profession", campaigners against changing the law have warned.
Robert Preston, the director of the campaign group Living and Dying Well, which argues against legalising the practice, said assisted dying was a euphemism for allowing doctors to kill people.
Speaking at a debate at the Law Society in London on Tuesday, he said most medical professionals did not want to be given responsibility for ending someone's life.
Under current rules the decision whether to prosecute someone who helps someone else die lies with the Director of Public Prosecution (DPP), who must take account of whether it would be in the public interest to pursue the case as well as look at the suspect's motivation.
The guidelines were established in 2010 after the House of Lords ordered the DPP to set out whether the husband of a terminally ill woman, Debbie Purdy, would be prosecuted if he went with her to the Dignitas clinic in Switzerland to help her end her life.
But some want to change the law to give people the choice of having a doctor help them end their lives in the UK.
Preston said the current law had the effect of "deterring malicious assisted suicide" and that changing it risked more ill people being coerced into ending their own lives.
"Most relatives are loving and caring, but some are not," he said. "Laws are not precision guided missiles...they have the effect of causing collateral damage."
It was better that the rules remained as they were, with "a stern face but an understanding heart", he said.
However he was challenged by Paul Bowen, the lawyer who acted for Debbie Purdy, said the current situation was unacceptable because it drove the practice of assisted suicide "underground".
Bowen warned that this meant it was impossible to know how many cases of assisted suicide were taking place in the UK and there was therefore no way of ensuring people were not being coerced into agreeing to it.
He said the current law appeared to say that "it's OK to have an amateur DIY suicide but not to have professional help".
And Baroness Young of Stone Old Scone, who was a member of the Commission on Assisted Dying, said people who wanted to have the choice to end their lives if they were suffering "intolerable" pain should have the right to be assisted "with professionalism not amateurism".
"Parliament should get off its bum" and address the issue, she said.