I think fast fashion is pretty awful, all around. Clothes are cheaper than ever (great!), but we're also buying more, lower-quality, more wasteful clothes than ever.
(One of the things that fascinates me about this trend is how bimodal the apparel market is: a reasonable but naive assumption is that economies of scale would also lower the cost for clothes made from nicer textiles - especially when manufactured in the same locations - but instead anything that's "nicer" than low-weight cotton gets a quality tax.)