As I've written a fair bit on this over the last 2 weeks, I think it's fair to share.
I've always been "your body, your rules" and pretty vehement about it, and always felt that people should have the right to die, and felt that assisting someone to do so should not be illegal, but it was a background thought. Informed and arrived at, but not spending much time at the front of my thought processes once reached.
First thoughts I was 13, my grandmother essentially made the decision to die, by suffering in silence and isolation with what she knew must have been cancer (she was a nurse) until we collected her for Christmas, but took her to hospital instead; metastasised to multiple systems, and absolutely terminal. Once there, she was either in agony, or away with the fairies and simply not her. She took about 6-7 weeks to die, and that in the days when doctors could prescribe pain relief even if it would reduce life-length (1990).
The one that really firmed my mind up that "something must be done" was my grandfather's death 2010 - kidney cancer.
His wife had died 4 years previously, he'd seen his grandchildren married off, and 3 great-children, and he was ready to go; but not to hasten the end - until the cancer.
He didn't have any fight left in him, and didn't feel he had anything left to live for - so he declined treatment for the cancer, and declined intubation for feeding.
The medical staff tortured him.
They took the view that if he declined treatment, then he was declining everything - they withdrew everything except a drip for hydration; coming in several times a day to ask if he was willing to receive treatment again, whilst he screamed and writhed in agony.
It took a couple of days and threats of legal action for the staff to agree to offer him pain relief, and try to arrange palliative care. Of course, he was gone before it could be arranged. From memory, he had about 36 hours of appropriate care, and about 3 days of torture - from multiple care givers - doctors, nurses & managers.
My grandmother would have chosen assisted dying, as palliative care couldn't have made her her. She was either in agony or an empty shell.
My grandfather would have chosen assisted dying (and did beg for release), but palliative would have been a valid option for him, as they were able to manage his pain without removing everything that made up him.
Obviously, these are not my only experiences - direct or otherwise. I'm a medical professional from a medical family (2 parents, 1 grandparent), and a mental health sufferer for... well about 6 years old is the first I remember trying to suicide (incompetently). The above are the most direct experiences in informing my opinions.