It should be perfectly reasonable for pretty much any combination of people, related or not, to decide to share the paying for and maintenance of a home, especially if it means they get to live in a nicer, more convenient place.
But I think if someone is going to live with their parents long term then, eventually, presumably quite gradually, there needs to be a shift from the situation where the parents are the carers and in charge of the child, to a situation where everyone is more equal. (Then perhaps beyond that you could even end up with a situation where the adult with the most responsibility, the one who is doing more of the paying, and perhaps even one day bringing a partner to live there too, is the one who was originally the child - a bit like the next generation taking over a family farm.)
That way you can still share a home while moving beyond the parent-child dynamic. I agree that living away from home (specifically living alone - I know people who've never done that either) is a really good experience to have, though.
Families pooling resources and possibly only running one household in times of financial struggle makes perfect sense - it's what families have always been 'for', partly - pooling resources and looking after each other, making economies by going in jointly, being close by and available for support.
I think there's a world of difference between sharing a house with family or parents, and 'still living at home', with all that implies about still being in the care of one's parents. Which you have is going to depend on the personalities involved (and probably also available space).