Why did he just kill people randomly when he was clearly raging against the rich people?
Well, he likened himself to Jesus Christ. His cause was clearly religious in his mind. Now, don't we all know about stories of religious figures or God's messengers coming down to Earth and taking some precious things from people that have sinned? Like someone's daughter, son or a wife? I believe this is very clear in holy ancient mythology.
Well, Cho felt he was a holy being that came to take away something precious, America's college students, for all the sins of the powerful people in this country.
Now, one thing on the media. Multiple people said something like: "He was trying to prove he wasn't a loser that he was." I don't know how anyone can call a college senior a loser!