The Patient (Assisted Dying) Bill is backed by the widow of Merseyside pensioner Reg Crew, a motor neurone sufferer who flew to Switzerland to commit patient-assisted suicide.
But Ms Curtis-Thomas, who has told how her paralysed mother changed her mind about wanting to be left to die, has insisted it sends the wrong message that "life is disposable".
Yesterday, she insisted most doctors did not support euthanasia, because they "feared the repercussions from family members".
Lord Joffe has argued his Bill would remove the fear that close relatives or friends could be prosecuted if they helped a terminally ill person make their journey to death abroad.
Merseyside Police spoke with Win Crew following her husband's death, but took no further action after establishing it was Mr Crew's decision to die.