Why do sasaengs try to hurt the idols? What's their purpose?

I obviously understand that obsessive fans are horrible... but I can somehow wrap my head around the concept of doing anything to meet your idol. But many stories about sasaengs are about trying to poison the idol or trying to hurt them.

Why would they want to potential unalive the person they supposedly obsessively adore? This is the scariest thing about them. How hurting them seems to be part of their purpose and I don't understand.