Sorry in advance, this is long:
No, I have no doubt that many, but not all, autistic people have just the same capacity to choose assisted dying as anyone else.
If we had decent levels of medical, social and palliative care in the UK then I would be in favour of legalising AD in the case of terminal illness with ~6 months or less to live, with safeguards in place to ensure patients had made a voluntary, clear and settled decision to end their life, with time to consider all other options. That would mean they had mental capacity to make the decision at the time of death, mandatory counseling, prescribed information, second opinions, high court for difficult cases. I have no doubt that many autistic people could meet those criteria just as well as I could.
That's not at all the same as saying we should allow AD because of autism, or learning disability, or mental distress.
Are you familiar with the swiss cheese model of safeguarding? No slice of safeguarding is foolproof, there are always holes. The more layers of safeguarding there are, the less chance there is that all the holes will line up. The more layers you remove, the more likely the holes will all line up and cause a safeguarding failure.
Allowing assisted dying at all removes a layer of safeguarding.
Allowing assisted dying for people who are not dying removes another layer.
Allowing assisted dying for LD, autism, mental illness etc., conditions which, by their very nature, require close attention to mental capacity removes another layer. And this particular layer seems to have a lot of holes.
A huge issue is doctors' ability to reliably and accurately assess people's ability to consent. Baroness Finlay:
The danger is that it depends on the ability of the clinicians making the assessment. I had the privilege of chairing the Mental Capacity Forum for six years. I have to say that it was worrying to see the inability of clinicians to assess capacity — particularly fluctuating capacity. Another group of patients where there is a real worry is where there is frontal lobe involvement in the brain, where they can appear as if they have capacity but actually they cannot understand the implications of their decision for themselves and others.
Only last week, I came across a clinical case of somebody in ICU, who appeared to have complete capacity to stop treatment. By chance, his girlfriend arrived. I won’t go into the details because it is a long story, but he then decided to marry her. Afterwards, he had absolutely no recall whatsoever of any of the conversations that had taken place when he had said that he did not want to be treated. At the time his clinicians — not just one, but three of them — thought that he was absolutely crystal clear that he wanted to stop treatment, and would have stopped his ventilation, but for the chance arrival of his girlfriend.
The potential safeguarding failure here is that you deliberately cause someone's death who did not want to die, who was coerced or persuaded against their best interests that they wanted to die, or who was not capable of consenting to being killed.
The stakes could not be higher.
How many of those kinds of deaths are acceptable so that you or your loved one can choose the time and manner of your death?
If there's the remotest doubt then the default must be that you do not take active and deliberate steps to end someone's life.
There are just too many layers of safeguarding missing for me to be comfortable with this, before even considering all the other missing layers of poor health care, poor social care etc.
I'd also be interested to hear what in your opinion exemplifies the Netherlands as an example of bad practice.
An example of bad practice in the Netherlands is when they held down a woman and euthanased her against her will. Details have been given upthread. Advance directives are not safe because people change their minds. In one study, 50% of terminally ill patients who said they wanted AD for themselves later changed their minds.
https://jamanetwork.com/journals/jama/fullarticle/193281
Also I think NL decision to allow assisted dying because of LD, autism and or MH issues is bad practice. The only reason they're not in a worse state than Canada is because they have decent health and social care. Long may that continue.
We don't, we're much closer to Canada in that regard.