We debate this constantly re my FIL. He is 94, with advanced dementia. He is very weak, sleeps almost all the time, hardly eats now - and finds eating physically difficult, so we now offer only soup and other 'sloppy' food. He is doubly incontinent, he cannot stand without help, has to be ferried around the house in a wheelchair. He cannot dress or undress himself, or wash himself. He has 8 hours of paid care every day, sometimes 2 people at a time, because that's what he needs. This is in addition to DH and I helping several times a week and the endless phone calls DH has to deal with, as FIL's care needs are changing constantly.
He cannot stay awake long enough to hold a conversation, and he cannot articulate his own feelings or thoughts, though in the few times he speaks, he is often angry and swears (pre-dementia, he was a kind, calm, thoughtful, gentle man who didn't swear). He is clear that he wants to stay in his own home though, and we are doing what we can to make that possible, and to try to retain some semblance of dignity.
His needs are increasing by the day, as his health declines. It's painfully slow, and painful to see. His death cannot be far off. We constantly ask what quality of life he has. DH certainly wishes euthanasia was an option.
It's very hard to generalise about making euthanasia legal. The devil is certainly in the detail.