In plain English, that's "introducing you to a product you wouldn't have known about otherwise", and yes, if they convince someone to buy a $99 T-shirt, this service had value for the buyer.
The negative externalities come from the fact that very few people will buy random unbranded $99 T-shirts on a whim, meaning they need to spam a million people to find the one or two buyers in the haystack.
It's not wrong tho. There are categories on AliExpress where there are like 20 similar products but only one does what you actually expect it to do.
Ex. Clothing sizing is a big issue there. Or real CE signs. If I have to compare 20 products myself and only add the good one to my store I definitely added some value for customers
Also as said somewhere else local customer protection laws apply to dropship stores, but not AliExpress
The negative externalities come from the fact that very few people will buy random unbranded $99 T-shirts on a whim, meaning they need to spam a million people to find the one or two buyers in the haystack.