Back in the olden days, chickens farmers let nature takes its course. The weak will die and the survivors will be stronger.
When my birds got something like this, yes I lost a few, the rest bounced back and are as healthy as a bird can be. They'll pass this strength on this to their babies.
This post reminds me of a horror story I was told. A young girl went to a show out west and was interested in RIR's. There was a breeder who is near 90, I don't remember his name, he has the pinacle of quality RIR's. He gave this little girl 8 chicks. One flopped over and croaked. She freaked and had it tested, it came back Mycoplasma. The young Vet told her to put down her whole flock and start over. She did. When the breeder heard about that he just shook his head. This case was one that DID NOT require killing off $500 worth of birds. If your birds can easily be replaced, it is okay. But, I just rather weed them out and let mother nature do the weeding.