From an animal cruelty standpoint, I don't know where this stands. To me, it seems pretty awful. I realize there is a spectrum of kindness-cruelty, and that animals have a spectrum of sentience-nonsentience. As for adult (and adolescent) chickens, they are pretty "reactive" - basically peck at anything to see if edible, and do learn their social structure. They appear to have fear. There's a reason that cowardly behavior is called "chicken" - they run away from almost anything but food. I have a friend whose hens follow her around the yard, but our hens are less sociable. Not sure why - my only contact with them always starts with treats, food, or fresh water.
Baby chickens eat & huddle for warmth. I don't know, if there is any way to know, if they are sentient in other ways.
Chickens are fun to watch, walking around pecking at stuff, eating, exploring their surroundings. I can't tell if they have a higher IQ than, say, a fish. I do think they are smarter than insects, but I can't explain why.
What do we compare to? Are they more or less sentient than a late term human fetus? Not to get into a discussion about abortion, and I support choice, but is it worse to quickly kill a freshly hatched chick? I don't know.
Anyway, knowledge of how meat, dairy, and eggs are produced are important in our choices. All dairy requires that the cows be bred, and half of their offspring are male. Male cattle don't get to live in the pasture and smell flowers like Ferdinand the bull - they are either castrated and raised as steers for the meat market, or go for veal. Fortunately, veal isn't very popular. The point is, milk production also requires killing animals - it's just that the milk doesn't contain the flesh of dead animals. Same for chickens, as in this video. Females go to the egg-factory and males are killed.
I've thought about this with my backyard hens. Since I live with an omnivore, and the hens are not really 'mine', and I think it would be hypocritical of me to say that all egg production is 'wrong'. On the spectrum of 'kindness-cruelty', our backyard hens get to live a much, much longer life, in much, much more pleasant circumstances, than their factory-raised kin. This is kinder compared to buying eggs at the store, but not without some guilt. Our hens came from hobby producers, and I don't know what happened to their 'brothers'. If I lived in a 100% vegetarian household, I probably would not have the backyard hens. Still, I do enjoy them, and I take responsibility in ensuring that their lives are pleasant.