Selection is not always about genetics in animals. There are also environmental conditions to consider. How a chick (or any animal for that matter) adapts to the environment is important. For example, if you want to breed chickens that lay eggs that are better at being handled rough, then you would not assist eggs that had been shipped. The chicks that developed would most likely come from eggs that were better adapted in their structure to handle rough conditions or low humidity. This is important to consider if you ever plan on selling eggs or chicks that will be mailed.
A good example is the Ayam Cemani. The eggs are notoriously bad at being shipped. I am talking one in a dozen will be develop (less than 10%). That's because breeders have opted to select for the blackest ones and not necessarily for the hardiness of the breed.
However, if you don't ever plan to sell or ship, or if the eggs were extremely expensive, you might ignore the survival of the fittest idea. I also say that every person needs to decide what their goals are for their breeds.