The absolute ban on assisted suicide deprives an "entirely innocent" group of severely disabled people of their right to equality and cannot be justified on the basis of "speculative concerns" about possible abuse of others if the ban was lifted, the Supreme Court has been told.
Fears of a "slippery slope" and possible abuse of vulnerable people if the absolute ban was relaxed does not justify the denial of the rights of Marie Fleming, said Brian Murray SC, for Ms Fleming.
The proper role of a legislative system is to provide safeguards to guard against abuse, he submitted.
In rejecting Ms Fleming's challenge to the absolute ban, the High Court did not apply the proper test in reaching its decision the ban was justifiable on grounds of a possible risk to others, he argued.
There was no proof of actual risk, he added.
The High Court had referred to a "substantial consensus" in western countries, shared by the Law Reform Commission, such an absolute ban was the "best approach" to protecting life and vulnerable people, he said.
That was not the correct legal test for the court to adopt, he said.
The correct test was whether such a ban impaired rights as little as possible and did not impose a disproportionate burden on one group.
Mr Murray was continuing his arguments on the second day of Ms Fleming's appeal against the High Court decision.
While suicide has been decriminalised, Section 2.2 of the Criminal Law Suicide Act 1993 makes it an offence to assist a suicide.
Ms Fleming argues the absolute ban should and must be relaxed to meet her particular circumstances as a terminally ill person in severe pain who is mentally competent to decide when and how she wants to end her life but cannot do so without assistance.
Ms Fleming (59) is in the final stages of Multiple Sclerosis and has said her long-term partner Tom Curran is willing to help her take her own life provided that is legally permissible.
A three-judge High Court ruled last month the absolute ban does not disproportionately infringe Ms Fleming's personal rights under the Constitution and is wholly justified in the public interest to protect vulnerable people.
The High Court also ruled the Director of Public Prosecutions has no power to issue guidelines setting out what factors she would consider in deciding whether to prosecute cases of assisted suicide. However, the court was however "sure" the Director would adopt a humane and sensitive approach to Ms Fleming's plight, Mr Justice Nicholas Kearns said.
Ms Fleming is not appealing against that aspect of the court's decision. Her appeal focuses on arguments the absolute ban on assisted suicide breaches her personal autonomy rights under the Constitution and European Convention on Human Rights and, in her particular circumstances, that breach is not justified on public interest grounds but is disproportionate and discriminatory.
The appeal continues.