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The group said it commended Justice David Collins on upholding the law, and agreed legislative change is the role of parliament, not the courts.
Ms Seales died on Friday morning, shortly after learning that a judge ruled her doctor could not assist her to end her life without risk of prosecution.
Renee Joubert, executive officer of Euthanasia-Free NZ, said she was relieved to read that Ms Seales had died comfortably, relatively quickly, and surrounded by loved ones -- "not the long, painful death she feared".
"The legalisation of voluntary euthanasia and assisted suicide is not merely a matter of individual choice and should not be based on individual tragic cases," Ms Joubert said.
"It's a major shift in public policy, with wider implications and unintended consequences for all of society that need to be carefully considered."
Ms Joubert said it was impossible to prevent abuse and coercion, no matter how safeguards were written.
"As a society we need to do everything possible to relieve people's suffering and ensure that everyone dies comfortably and with dignity. However, this legislation is not the solution. It's simply too dangerous for society."
Meanwhile, the Anglican Church in Aotearoa New Zealand said Ms Seales' death was a time to acknowledge her courageous determination to give focus to an issue requiring wider debate.
Archbishop Philip Richardson said the church was committed to engaging with the debate, which raised issues of deep significance for humanity.
"Whatever our views, part of Lecretia's legacy will be to refocus this public discussion."
Archbishop Philip said Ms Seales and her family were in his thoughts and prayers.
"For the moment I simply want to acknowledge Lecretia's passing and the loss this is to those who love her most. To them I offer the assurance of the prayers of the Church and our condolences."