It seems to me it would be a cheaper build and structurally sounder if planes did not have windows. Perhaps cameras could be linked to LCD screens for a view of the outside.
I remember in “From the Earth to the Moon”, the episode SPIDER, the designers spend a lot of time fretting over the weight of the windows. With today’s technology, are windows necessary?
If they didn’t have window seats there would be complete mayhem at check-in as absolutely everybody is going to want an aisle seat. As it is there are still some of us childish enough to prefer a window.
By now it’s probably more tradition , people expect them. Most kids really like them.
Windows have NEVER been necessary on planes (apart from the ones in the cockpit;)). But people demand them, so there they are, despite the fact that they weaken the fuselage and add to the weight. Likewise, it’d be safer for the passengers if the passenger seats faced backwards; but the passengers want to face forwards.
At least, that’s what the aircraft designers say. I’ve no idea if they’ve done any research into this.
Well, as I said, are cameras with LCD screens not an option? Even for the pilots?
Why does anything have windows? Houses, cars, buses, cruise ships, jail cells… questions of cost and structural integrity aside, people generally like being able to see outside and to have some natural light so as to not feel so trapped. Why would planes be any different?
ETA: LCD screens, at least for the people currently alive who grew up in the “real” world, generally aren’t sufficient. It’s the difference between a screensaver and actually going outside. Maybe in a few generations.
It’s not a technological issue but a social/psychological one.
In the theoretical world, windows are not needed. In the real world, they are needed.
Human behavior and all that.
Lots of added cost to put them in for the passengers, and you know, I’d be very reluctant to fly on a plane where a power failure means the pilots can’t see what the plane is doing. I bet the pilots would be reluctant too.
Just take a quick look at pretty much any military troop/cargo carrying plane in existence. Nope, no windows other than for the cockpit and where absolutely necessary.
Those guys are getting paid to travel to an insertion point. We, OTOH, are paying to look at the clouds and the sunset. 
I forget where I read this, but a book (Cadillac Desert?) opens with something to the effect of ‘anyone who flies cross-country and doesn’t spend the majority of their time staring out the window has wasted their money’.
Pffft. Once you’ve seen one square state from 30,000 feet, you’ve seen them all.
OK, I’ll grant that there’s nothing to see in Nebraska other than the Platte River Valley, and nothing whatsoever to see in Kansas. But to claim that Colorado or Wyoming has nothing to see? Are you flying over the same states I am?
Just because the borders are boring doesn’t mean the contents are.
I am questioning how an LCD screen with cameras for each passenger is cheaper than “hole with plexiglass in it”.
Plus, the fuselage of an airliner is just a big tube. It’s barely pressurized and not under all that much stress. There’s no reason to worry about the structural disadvantages of windows. Wings would be another matter, but the fuselage, no big deal.
ETA: I take umbrage at your suggestion that Kansas and Nebraska are boring because they lack mountains. There are plenty of other things to look at. The view of those states is not appreciably different from the air than any other state except for the mountain ranges and maybe the coastlines.
Maybe that’s why I never went in to the military, especially submarines. If someone tried to lock me into a tube, screaming through the air at 500 MPH, over 6 miles in the air, I’d crap myself.
There are a lot of 747s and 757s and so on with no windows - they are owned by DHL, FedEx, UPS ,etc. I wonder how much cheaper the cargo versions are - they also have no seats and are missing other stuff too
Not only are most military cargo planes short on windows, they also have the passenger seats facing backwards.
I’ve flown on USAF C-5 and C-141 cargo planes, and both were dark, noisy, and you flew backwards. I wasn’t getting paid to fly, but I did get a round-trip flight to Germany for free.
At least the pilots on a plane can see where they’re going.
In a submerged submarine, nobody can see outside. All you have are passive sonar displays. Picture a blind man walking along and making his way by listening intently.
Then there was the time that our main onboard computer crashed and had to be rebooted. We were completely blind and deaf for what seemed like a very long time before the displays came back up.
Many of the cargo planes are converted passenger planes so they retain the windows but are covered up by interior wall.