I think a lot of people have personal preferences that they feel compelled to justify morally in some way in order to rid any cognitive dissonance that could happen. So they make up reasons that it's "-ist" to be against what they like, so that they can feel good about themselves while in their own head thinking they are making the "best choice". For example, people who don't like bike lanes saying that bike lanes are ableist. Or in this case, someone who likes fast fashion saying that it's classist to be against fast fashion.
It's okay to have preferences. You don't have to justify morally literally every single thing that you ever do. And you especially don't have to say that anyone against your preferences is, in some way or another, being unjust.
It's okay to have preferences. You don't have to justify morally literally every single thing that you ever do. And you especially don't have to say that anyone against your preferences is, in some way or another, being unjust.