Charlie regularly received death threats. Implicitly or explicitly telling him to quit or else. He had the courage of his convictions and refused to change his beliefs or be deterred from acting on them.
His haters martyred him. Like Justin Martyr, who refused to change his beliefs and worship pagan gods, and who kept to his course despite being told he would be executed if he didn't change.
One thing that history shows again and again is people being killed for their beliefs. Charlie always spoke from his heart, from his deeply held intellectual and spiritual beliefs. He died, literally on a stage defending those beliefs.