I can afford retail but I do quite a bit of clothes/accessories shopping at the thrift store, because I have a passion for collecting vintage clothing, costume jewelry, clutches, etc. I don't shop at chain thrifts like Goodwill or Salvation Army (I've just never been to one) but at hospital-affiliated shops in and around my hometown. Thus, every time I purchase something there, I am donating to the hospital (all clothes these places sell are donations and the stores are staffed by volunteers, so all money goes right to the hospital). Of course, when I am shopping in this store, many of my fellow shoppers appear to be shopping there because they cannot afford much else. But are these shoppers buying the same things as me? No. I buy crazy costume jewelry, vintage mini-dresses, gorgeously impractical things.
There are more than enough secondhand goods to go around in this world, so that both the people who need to buy in thrift stores and people who want to buy in thrift stores can both do so.