I think that your perspective might have to focus on why physician- assisted suicide is not acceptable in any condition. It seems like much of what you will be saying will apply to all nations, and not only Australia because you would be embracing moral universalism. I would think that the bulk of your speech would center on the violation of the Hippocratic Oath that the physician cannot take a life. The Hippocratic oath states “I will not give a lethal drug to anyone if I am asked, nor will I advise such a plan." It seems to me that this is the crux of your argument. It becomes difficult for doctors to be the healers of the body and spirit if they enter a realm where they start to take life. The other argument that has to be made is that if an exception is made which allows the taking of life in one setting, the slippery slope risk is present:
Another reason for prohibiting PAS and euthanasia is the option of abusing PAS if it were to become legal. Poor or uninsured patients may not have the money or no access to proper care will have limited options, and they could be pressured towards assisted death. For emotionally and physiologically disturbed patients, they could abuse the PAS option and those patients could convince their doctor to help end their life.
In my mind, your speech might have to revolve around both of these points.