I agree with you OP.
No one is obliged to provide care. You can refuse to get involved with the care of a parent.
There are lots of incurable diseases that are awful in the final years, months and days. Some diseases are harder than others. Are we suggesting that any disease that makes it hard, the person should just off themselves out of a sense of duty?
And if not every disease, then which ones are ok? And who gets to decide what level of frailty of dependence isn’t too much of a burden?
Getting old and sick is awful. If you personally want to avail yourself of Dignitas-type services, or even do a DIY job, that’s your choice. I don’t think anyone is disputing that.
But saying to your parent “if you start to become a burden I expect you to kill yourself” - I think that’s absolutely awful. None of us owe another person the duty of killing ourselves.
And when do you do it, exactly? While you’re in your fully aware state? Well that’s great but you might end up losing months or possibly even years of an enjoyable life. And why should you have to give up the most precious thing any of us have just to avoid inconveniencing others?!
But if you wait until your disease starts to progress, you’ll lose your insight and awareness and probably won’t do it. It’s really not as clear as people seem to think.
And just for full context, I cared single-handed for my dad until his death from Huntington’s Disease which in his case, included aggressive dementia-type symptoms from very early.
And I now care for my mum who has cerebral palsy and mixed-type dementia. She lives in my annexe.
So I say all of this with a very intimate understanding of what it’s like and what’s involved.
I imagine the sister was speaking from grief, so I’d cut her some slack for that reason. But her mum is obviously grieving too and I think the sister has been pretty thoughtless here.