We do allow it in certain states/countries. But when it comes to dementia, it's a difficult question. A person's mind is shattered by the disease. 2 years befor

We do allow it in certain states/countries. But when it comes to dementia, it's a difficult question. A person's mind is shattered by the disease. 2 years before death, they might say "I want to die when I can't remember my childrens' names". Then 6 months later, they turn into a completely different person, forgetting everyone and refusing to see a doctor, let alone give the necessary consent to allow someone to administer the final drug.