I think someone said (many pages ago) that Moderns would do well with plenty of dry hay to snuggle down into for warmth.
I agree that we can overprotect our birds and eventually weaken their system's genetics.
A Poultry magazine article several months back gave this information on keeping chickens during freezing weather: Keep them dry, provide a windbreak, make roosts available in the dry, fresh water and good feed. The author said fresh air is necessary to remove the ammonia gasses and moisture from the roosting area...more dangerous to the birds than the cold. He said many of the respiratory issues with our chickens come from the ammonia and moisture rather than the cold. Pictures showed screened doors exposed to the south that allowed in the sunshine and fresh air. They were not blocked and there was snow on the ground. He did say that during harsh winds or blizzards, he would cover the doorways with shutter doors.
I'm still an old softy at heart and try to "rescue" one of my birds when it is ill. I treat it first in the hen house in a quarantine pen. If that doesn't work, I will bring it in....I'm finding that those usually don't make it. My MIL who raised 1500 chickens at a time, said you have to get tough and culling a sick bird is more humane and safer for the flock.