Here is an excerpt from an article from lubavitch on this practice. Can anyone confirm the accuracy of these referencs, and if so, how can we continue to use the chickens if these two great leaders condemn it?
“””Some Rabbis Condemn It
The practice of kapores has created a certain amount of controversy amongst rabbinical scholars. The Ramban, also known as Nachmonides who lived from 1195 to 1270 CE criticized it as a supersticious practice of the Emorites, one of the neighboring pagan peoples to Israel. Later Rabbi Joseph Karo (1488 – 1575 CE) also criticzed the practice in the Shulchan Aryuch (Code of Jewish Law). While there have been communities that do not practice the custom, many of the Rabbinical authorities did support it and encouraged its practice. Despite this controversy, kapores is practiced by many in both Sephardic and Ashkenazic communities.””