He chose his beliefs over his boxing career.
Pm Carpenter on Muhammad Ali:
He was so much more than boxing's "Greatest"; he defined and moreover impelled the domestic turbulence of the Vietnam and civil rights era. He was, as well, a bundle of paradoxes: a gentle man in the most brutal of sports, a semiliterate who out-imagined the best and the brightest, a victim of racially structural rot who refused to be victimized.
Muhammad Ali on why he refused to fight in Vietnam:
"My conscience won't let me go shoot my brother, or some darker people, or some poor hungry people in the mud for big powerful America. And shoot them for what? They never called me nigger, they never lynched me, they didn't put no dogs on me, they didn't rob me of my nationality, rape and kill my mother and father... Shoot them for what? How can I shoot them poor people? Just take me to jail." -Muhammad Ali