I hear these stories and think "if they just had one friend, it could have turned out differently"
But Rodger
had friends. It's true he was teased in school, and quite mercilessly at times, but he had more than one friend throughout his life. The problem was that his delusions and rage became so intense that he pushed the people he did have in his life away. Based on the content of his manifesto, Rodger constantly compared himself to his friends, and to other people. And whenever he saw any one of his friends socializing with a girl when he apparently could not, he would become upset. Eventually it got so bad that he would make a scene everywhere he went if he happened to see a girl, or a happy couple. Let me give you some specific examples:
Rodger tried to get along with a roommate he had, and did, for a time, but once he saw a girl leaving his friend's room, that was it. He couldn't stand the guy after that because the roommate had apparently had sex and he didn't. He was enraged that someone heavyset and shorter than he was had been with a girl. So he contented himself with thinking that she was an ugly whore, and that he would surely find a tall, blonde, sexy girlfriend instead of someone like that young lady.
He claims several times that he tried to talk to women, but there's not much evidence of that. He does mention being ignored by a few specific people, but the rest of the time he was too crippled by fear and self-loathing to do anything much beyond play World of Warcraft. When he did feel more inclined to try and attract female attention, he thought he could only do it by having the fanciest, most expensive possessions---the fastest cars, the finest clothes, and so on.
His obsession with sex and, more generally, with being adored, completely blinded him to the people that were in his life and trying to help him. His parents hired specialists to try to teach him how to socialize properly, but he resented that. Apparently he also refused to take the medication his psychiatrist had prescribed (which is, of course, his right, but that's not the point). Every time he met someone new, he would ask, "Are you a virgin?" If the person being asked said no, Rodger would fly into a rage and curse.
He hated his parents for not knowing how miserable he was, but he didn't try to talk to them about how he felt. He even planned to kill his little brother, whom he'd once saved from drowning, for apparently having the kind of successful life he'd always wanted. And Rodger's last remaining friend, James, was essentially scared off when he was told of fantasies of killing women and stripping the flesh from their bones. But as isolated as he made himself, people were still trying to help him, right up until the end.
I'm not sure that all the friends in the world would have been able to satisfy his need.