Here’s one whole thread on dementia and self-euthanasia.
And another that starts on a different topic and morphs into the same topic.
In both of which a lot of people agree they’d totally prefer to kill themselves than suffer through the end game of dementia. IOW there totally are righteous suicides.
What those ~200 posts also demonstrate is that our society has some severe hang-ups about what ought to be, for those of at least semi-sound mind, a completely acceptable personal decision.