In India, it is a common practice for adults to live with their parents. Why is it frowned upon in USA? Is it a good practice?
Ahh. Culture. I think its less the fact that you're living with your parents, than why.
In india, in general you live with your parents (or live with you) often so you can take care of them. There's also a very different expectation of "private space" - kids tend to share rooms from what I've seen. You eventually move out when you get your own family, but at some point, grandparents move in and a extended, multigenerational family was a norm, least until very recently.
(In this case I'm speaking broadly. Please feel free to correct me in the comments) In the US, I'd suspect there's a perception that you're living with your parents cause you can't move out. You may have a job, but there might be an idea that you're being at least a bit parasitic, or co-dependant with your parents.
That said, I do live with my parents, and the attitude between how people react to me when I was working for my folks (or as many assumed, not at all) and when I work elsewhere is very different. At some point I'm moving out (tho, I live in a small country), and while I'll be up to some stuff my parents wouldn't approve of in their house (like finally getting a small lathe!), I'll likely maintain fairly close links with them.