I only ever hear about Shein in a negative light. It's never been entirely clear to me why Forever21's and H&M's disposable clothing is somehow morally superior to Shein's.
Anecdotally, I have heard that there is three towns where a predominant amount of Shein clothes are made and while people are free to leave, they’re paid in “company bucks” akin to company towns in the late 1800s/early 1900s US.
If you're buying a t-shirt for under $20, forced labor is probably somewhere in the supply chain.
The expiration date on clothes is so short that now transporting it by boat is not too slow, and they have to take plane.
(writing this post, while wearing 4yo jeans, and 5yo t-shirt)
Fast fashion gets a bad rap because of the assumptions about consumer behavior and labor. Almost all clothing is terrible for the environment and for the people manufacturing it, anyway. I have many H&M items that are nearly a decade old and are still wearable.