This isn't only about breast milk for prem babies, or even for babies.
Read the articles linked above.
It's about breast milk for mothers who couldn't BF or can't (perhaps because, like in America, they have to go back to work really early) - but also it's about people like body builders and other health nuts, buying breast milk to drink, themselves, as they think it's good for them.
Yes, there's a discussion to be had about breast milk for babies and how, for example, it can save lives if donor milk is used in NICU.
But, this if we're talking about the commercialisation of breast milk, then just focusing on prem babies is obscuring the reality of what's going on here.
This industry is about exploiting women's bodies for profit - and it will be disproportunately, impoverished and vulnerable women's bodies - being used to make what is essentially a cash crop. Like a cow, or a goat, if you like.
I read an article a few years back about a company that encouraged women to supply their milk, talking about how it could really help babies - but they didn't make such a song and dance about their other customers - adults buying and drinking their milk as a health suppliment. Would the mothers have been so willing to sell their milk if they'd been aware it wasn't all going to babies? Possibly not.
Breast milk fetish is a thing, also, and if human milk is available on a simple commercial basis, you can't really stop pervy men buying it for their wanking / sex game obsessions.
The bottom line is, should women's bodies be used for commercial profit like this?
To say they have a choice is exactly the same argument as sex work. For some, OK, yes. For many, probably not. Especially if the breast milk is traded internationally.