Psycho shooters

Charles Whitman knew there was something wrong with him. Instead of seeking help, he decided to go on a shooting spree. He also mentions in the movie how he doesn't want to live anymore. Why do all these psycho shooters want to take other people down with them? These weren't even people that Whitman knew or that wronged him. It was just random victims. Was this his way of getting his kicks before he died?