They're not environmentally friendly when compared to natural hemp shoes, etc -- but they are no more harmful than leather. Aside from the animal rights aspect tanneries reak havoc on the environment. Faux shoes, like those at payless and target are from man made materials which is kind to the animals but some of the chemical used are pretty harmful. Many also come from sweat shops in china... though I do buy and wear payless shoes -- they are fashionable, affordable cute and vegan. Maybe some day I can afford the eco-friendly vegan shoes too.
I agree that the man-made materials are probably not too great for you, but anything is better than leather. Also, DSW usually has a fair selection that are man-made, but it takes a lot of label reading since a lot are made with leather. I got a really cute pair of dress shoes for $40 since I couldn't find anything at Payless, Target or Wal-Mart