It does sound awful doesn't it? But understandable. Some people have been known to think this about old sick whiny clingy pets too. It's a horrible feeling, with such wrenching guilt.
Parents get really hard work when they're getting much older, and can put a real strain on middle aged adult children, who often have a job, children at home, the menopause, life struggles like financial issues, cost of living, soaring energy bills costs etc, and other commitments.
Having very clingy, needy elderly parents on top makes life very difficult. I have witnessed 3 or 4 people (over 75) who are unable to get about without lifts from their adult children, (and they need to go somewhere at LEAST once a week, often twice or more,) and they are very needy, and complain about everything, and they demand the children visit them 3 or 4 times a week and take them EVERYwhere.
I also know a couple of people who are housebound, need adult nappies, and need every meal cooking for them, they keep falling over and bruising themselves, and are taking about 15 different types of medicine/drugs, and I know a couple MORE who have an ambulance every other week!
All their adult children are at their wits end. As for the ones who are very sick, and being put through shit loads of treatment, and have zero quality of life, we don't allow this with animals/pets, why do we allow it with humans? WHY? My DH has a theory that they just use people to experiment with drugs to further medicine. Maybe he's chatting shit, but they might be! If that IS true that is horrific. But even if they're not, it's still awful to drag someone's life out when they are clearly suffering.
I think people will think the same about a husband or wife who is like this too. I know a woman whose husband developed dementia at 52. A really fit and healthy man up to 50-51, then went downhill sooo quickly. He was a really needy whiny clingy mess, and she said multiple times (about 2 or 3 years after he first started to get bad,) that she often wishes he would die - as everyone's life around him - including HIS - is just miserable.
I also have a friend (aged 30,) whose nan (aged 78,) was diagnosed with dementia 2-3 years ago, and she is a crumbling wreck now, who doesn't recognise most of the people around her, and cannot take care of herself at all. She hasn't been able to look after herself for about a year and a half, and she gets passed from family member to family member, (to stay with them for a month or so at a time,) as no-one wants to take her on full-time. She has 4 adult children, (all in their late 40s and their 50s,) and 6 adult grandchildren - in their 20s and early 30s. The poor woman gets shoved from pillar to post, with every last family member just wishing she would die.