Is it more unpleasant to be together or apart? I think it's a spectrum, and individuals' preferences can vary widely on that spectrum. But there must be tendencies, averages. People who manage populations of humans should be aware of these.
I was looking today at pictures of prison cells from around the world.
Philippines
Also Philippines, inmates sleeping on a stairway:
According to the United Nations Standard Minimum Rules for the Treatment of Prisoners ("the Nelson Mandela rules"), indefinite or prolonged solitary confinement is a form of torture. They define solitary confinement as "the confinement of prisoners for 22 hours or more a day without meaningful human contact," and prolonged solitary confinement as any solitary confinement that lasts more than 15 consecutive days.
I don't know about you, but I would prefer three months in the Denmark cell with a couple hours a day out for showers and exercise over three hours in one of those Philippines prisons. Even the Canadian cell would be more tolerable. All the others besides the Philippines look bearable to me, if I could have the room to myself. But I suspect that even in the Denmark room, if I had to share it with someone--even someone I liked--I would pretty quickly grow either irritated by them or afraid of them.
This isn't because I've never shared a room. In Army Basic Training, I was in a room with 15 other recruits for 10 weeks, but we didn't spend our whole day cooped up in there together. In college, I was paired with a roommate, but we didn't spend much time together. I spent much more of my time hanging out in the room of a friend down the hall. But even we didn't stay there. We went for walks together, and we had lots of time apart. Even when I shared an efficiency (one room and a bathroom, no kitchen) with my girlfriend when I was 18, I still took walks by myself to the grocery store or with my college friends. If we'd been confined there for 22 hours a day having to watch each other use the toilet in the same room we slept in, we'd have probably been ready to kill each other.
In the Facebook group where I saw these photos, people were leaving comments about how some of these cells are superior to small apartments in various large cities that go for $1,000 - $3,000 a month, with many joking that they now aspire to be a Scandinavian criminal.
They're not wrong to make these comparisons. When I walk among the skyscrapers downtown, and I look up, thinking of small apartments crowded together and stacked up, row upon row for tens of stories, I'm filled with dread. It's a horror to behold! It reminds me of battery hen cages stacked up in egg barns, only worse. 
Hangzhou, China
St. Petersburg, Russia
Columbus, Ohio, USA
In all of these, the greatest discomfort is the feeling of never having privacy, of always having strangers living just on the other side of your walls, floors, and ceilings. Even in a duplex or row house, where you might have the luxury of a yard and a porch, you still deal with this. They're just larger, more luxurious jail cells. I look at all these pictures, and the only real difference I see between apartment, dorm room, and prison cell is the rules and freedom to leave. The accommodations themselves are strikingly similar--four walls, a ceiling, and a floor, with space to sleep and sit, a toilet, a sink, electric lights, a window--all crammed together as tightly as possible without regard for the human need to have a bit of space between each other.
Today's suburban homes are scarcely an improvement:
Go out to mow the lawn, and everyone within a square mile hears it. Get a package delivered, and 50 otehr households know about it before you do. Drag your trash to the curb, and the whole street knows exactly what time you did so. Unload your groceries from your car, and anyone who looks out their window knows how much you bought and where you bought it. Not friends, but strangers, maybe even enemies, can observe you as closely as any stalker or detective without ever leaving their own home to do it. And people aspire to this! They call it "success" and "comfort" and spend half a million dollars for the privilege of being a fish in a bowl, up to their armpits in their neighbors' presence, having to ask strangers' permission to put up a decoration or cut down a tree. To me, this is punishment--the same kind as prison. It's just a question of degree. From my perspective, this suburban picture and the pictures of the Philippine prisoners are just different amplitudes of the same phenomenon, one that I find abhorrently oppressive.
So what's the alternative? The opposite, right?
But then we're told that loneliness is an epidemic, that isolation is unhealthy, that it's both a cause of and a symptom of mental and physical illness. We're told, "It takes a village," and "No man is an island," and all these other platitudes meant to convince us that sleeping with 100 criminals in a stairwell is preferable to the solace of quietude. I don't buy it. A person can feel lonely surrounded by a million strangers. But when those strangers are boisterous or bellicose, the only peace to be found is in getting away from them, out of sight and out of earshot.
But this can get lonely, and it also leaves one vulnerable. Roving bandits can easily prey on a hermit. We don't leave old people alone because they might slip and break a hip, or forget to turn the stove off. They need someone to keep tabs on them for their own safety. And so we withdraw from the teeming throngs of the unwashed masses and create remote, rural compounds that admit only the closest and most trusted friends and family, if we have the means. But others get the same idea, and soon the rural paradise turns into just a larger version of the rural subdevelopment. You might have a few acres between you and your neighbors, but you can't look out your window without seeing a dozen houses; can't open that window without hearing their music and conversations and motorized toys.
There must be a happy medium, a sweet spot, where we're just close enough together and just far enough apart...but I don't know what it is. I'm not even sure what it is for me, and I'm sure different people have different preferences. I suspect, though, that whatever the perfect distance is for our mental health, it's farther away than the engineers would like to put us for efficiency of materials used in building infrastructure. It'd no doubt be cheapest to house us all in a single, massive warehouse like broiler chicks.
