Originally Posted by
Pilot DAR
I have approved ex freighter Cessna Caravans (no cabin windows) to carry parachutists. This was accepted by the authority, though with a sidewards glance (pun intended). I'm not aware of a design requirement stating that there must be windows for passengers to look out, but I think it's fairly widely agreed that passengers might not like the ride, if seeing out is impossible.
Most passengers in a wide body don't have a window view anyway. In the modern era of seat-back video displays, it might be enough to have a seat back display where every passenger could pan around the plane for outside views, fed by external cameras. Or heck, everyone gets a VR headset if they want to see outside, or what the pilots are seeing. Then you can save weight on the fuselage and reduce impact hazards with windows.
Where that gets dicey, is an in-flight or landing emergency situation, where the displays go dark and the pax are in a sealed cabin with no external view for anyone to know what's happening. Recipe for panic.