We all need friends. We can agree on that, can't we? That having friends is A Good Thing?
Having friends is part of the human experience. We all have family, yes, but family is (in theory) loosely obligated to us by dint of shared blood. But friends? Friends have no such obligation. They do shit for you because they like you, not because they have to. Need to commiserate over a beer about a lost love or a bad day of work? Call a friend. Want to share your triumphs or exploits? Call a friend. Have a dead body that requires help with dismembering and dissolving in quicklime? Call a friend.
Friendship is a critical part of mankind's ecosystem. It is the grease that keeps the very wheels of civilization rolling - without such mutual admiration and camaraderie, this train will likely break down in a cloud of steam, the engine collapsing into a pile of clanging debris. Friendship is part of our connective tissue.
Unless, of course, you're a character in a videogame.
Here's what doesn't happen:
I'm a known Spartan. Or maybe just a nameless Orbital Drop Shock Trooper. Prepping for the scene of battle, one of my cohorts - another Spartan, a soldier, an ODST - comes up, claps me on my rattling armor, maybe gives me a head-butt like they do in football, then tells me, "It's good to see you again, man! Last time I saw you, you were drunk in a bar in New Mombasa!" Or he talks to me about how we used to cruise for chicks. Or he wants to know how my sister is doing.
I'm an American Marine. We're holed up in a house in the middle of a Virginia suburbs - suburbs that have been wrecked by the Russian Invasion of the United States. While we're crouched down by the windows, waiting for our chance to move out, another Private First Class is like, "Ramirez, man, this looks like your house, doesn't it?" And he talks to me for five, maybe ten seconds about that time on leave when he came over for dinner at my house. Or he talks about how when we're all done here (meaning, if we live through the assault), he's going to drink my ass under a table. He makes me care about him in just a few lines of dialogue. Lines of dialogue that implicitly establish the bond we share - not just the bond of war, but of something that goes beyond the battlefield, that goes beyond the Corps.