I have nothing against choosing a planned or assisted suicide when my suffering becomes unbearable. Incidentally I saw a counsellor a few years ago and recently learned her father died by a planned suicide when his physical pain became untreatable and unbearable. My counsellor knew it was going to happen. It was very hard for her but she respected his decision and supported him. She said it was still a shock to her when it actually happened.
We care for our pets when their suffering is too great. I think human beings deserve the same compassion, especially when they can clearly and coherently decide that is what they want for themselves.