No solitude is not healthy. Only our shitty 21st century individualism pushes from industry and media have shifted things in that direction and almost nobody is happy doing it.
Suicide is also something people choose. Being killed is something that happens to them.
If a person suicides to not be torced and then killed my the enemies. How is that different from choosing soltitude over loneliness?
Or to your more visceral examples: Medically assisted suicide could barely be called a choice (there are hardly any options with less painful outcome), but a suicide to avoid being hurt by others against your will is definitely even less of a choice.
This is not how it works in the real world.
Consumers are blasted with manipulative ad but still they've a choice, it's no more different than a suicide.
There's the kind when I'm absorbed in a book. Far from feeling alone, I feel get caught up in the story and sort of feel like a participant in an imaginary world. It doesn't feel like solitude at all.
Then there's the kind when I'm "in the zone" working on something. I loose track of time, people, and surroundings and when I finally figure it out I feel really good.
The rest of the time I'm just alone and lonely, and that's a bad thing.
Whatever the reason, spirituality, philosophy, art, to name a few, people have decided to live alone since at least recorded history...
I'm not sure this trend can be extricated given family units have become smaller over time as access to medicine and education has increased.
It's not a product of capitalism or democracy, (or communism or authoritarianism); it’s a product progress --how we deal with this modern phenomenon remains to be seen, given this is a pretty recent development (a 20th century development).
Try writing a politically incorrect comment here and see instant refutation followed by downvotes.
People are not good at coming up with morally correct statements in a realtime situation, they don't want to be shunned by saying something unpopular. It's better to giveup on your own terms then be ostracized by a group.
They avoid interactions.