Here's my two cents for what it's worth.
I have had chickens in confinement and free range and mine are happier with as much open space as possible. I think the biggest issue that I see is people trying to cram in too many birds in too small a space. When in doubt, go with less birds. I had 8 birds in a 10x10 run that were allowed to free range when I was home to watch them. That being said, I also would pile up 3 feet of leaves from the woods behind the house in the run once a month for them to dig in and scratch through and they would be happy campers. I also periodically brought in branches and fallen trees for them to climb on inside the run so that it was never the same configuration for too long. It kept them from getting bored and they seemed to love exploring the same old run every time I changed it up. They also had treats, scraps, a pan full of sand to dust bathe, and lots of fresh water and bedding at all times.
When I got the itch to have more birds I knew I either had to make a bigger space available or get rid of some of the older birds. We were lucky enough to be able to move to a piece of our family's farm and now we have a run that is 80ftx110ft and they are happy campers. Part of it is wooded and they love having the leaves and underbrush to scratch around in. I also have 4 ducks in there with them but in a separate house and everyone is happy. 4 ducks is my limit...I have more when they have babies every year but I always try to get back down to my original 4. Yes, my run is still full of grass. The most I have had in there is 12 chickens but now I am down to 5 hens (until spring when I plan on adding 5 more) and the 4 indian runners. I do clip wings to keep them from flying over the fence but they are happy and so am I.
You can tell when an animal is happy and content....you can see it in their eyes and their body language. I have 37 cornish x's in a tractor now but I know they are happy cause they get moved to fresh grass every day, they peck around and scratch like "normal" chickens, and they genuinely seem content with the fresh air and space they have. I know the limits of my space and I don't exceed it.
I am all for having chickens for eggs if you can provide them with adequate space for the number of birds you intend to keep, clean living conditions, safe shelter, and a constant supply of food and fresh water. If you give them all of that then go for it, just don't cram a bunch of birds in a tight space and leave them and expect them to thrive because it won't happen.