The wulin as written about by wuxia authors such as Jin Yong, Gu Long, and Leung Yu Sang was largely fictional, but there was something of a "wulin" society in history...martial artists who worked together as anti-government rebels during times of foreign domination (such as during the Yuan Dynasty and Qing Dynasty). If the stories told in wuxia novels are to be believed, these warriors were known for their heroism and chivalry: they used their great fighting skills to protect the innocent and uphold justice. Their methods were violent, but not directed against innocent people. These were xia.
From these anti-government martial societies evolved the organized criminal enterprises known as "triads" today. Although the triads have their own code of honor, ordinary people would not regard triad members as "chivalrous." The triads are thought of as felons...bullies who use violence or threats of violence to extort and exploit innocent people. They are not thought of as heroes.
So how did the "chivalrous" wulin society devolve into the "vicious" triad society?