Craigslist isn't the problem. No matter where you advertise, once you let go of the chicks their fate lies outside your hands. For example: someone may buy them, intending to keep them as free-range laying hens, with the best of intentions, then end up selling them to someone else who will slaughter them.
Many years ago, we sold a dog for $200, to people whose home we visited before completing the transaction. We exchanged e-mails for quite some time, getting updates on the dog. After awhile, they stopped corresponding and we learned through a third party that they took the dog to animal control when finances forced them to move. We were devastated as we'd made it clear that we would buy back the dog if there was ever any problem, and surely they could have sold the dog or adopted her out themselves with minimal effort. She was young and AKC registered. Since then, I've learned to live with the hard truth that once I let go of an animal, it's fate lies outside my hands.
I always do my level best to ensure that I thoroughly question anyone who buys or adopts an animal from me and I trust my instincts. I never give an animal away unless I know the adoptive individual or family, as I believe a financial investment, whether sale or adoption fee, will help ensure a good outcome. Not always, but more often than not.
I have sold pullets and hens on Craigslist. I always ask people what they intend to do with them. If it feels right, I complete the transaction. In the end, when dealing with farm animals there's always the risk, even likelihood, that they will eventually end up eaten.