“Terrifying”? Perhaps you are over-reacting. People (including men) of nearly all ages (although reborn dolls are not recommended for small children) collect reborns and/or are artists themselves. I fall into the latter category. I really do not think that there should be concern for the young people who have not started families. As you are a parent, I think you know that child-rearing is a learn-as-you-go experience.
I began my interest in reborn dolls one year ago. They are the type of doll that I had always wished was available when I was a girl. I might also mention that I have raised five living, breathing children of my own, and now have five grandchildren. I also take care of my youngest grandchild while her parents are at work.
Reborn collecting/artistry is a hobby, just like any other hobby you may name. Any hobby has its elements of expense.
I should also mention that I am a retired Gerontology RN. My nursing specialty does use reborn dolls to calm the Dementia patients, as you have mentioned.
I might suggest that if reborn dolls give you the heebie-jeebies, then they are definitely not for you. I`m sure that there is another hobby out there that you will enjoy.