On April 4th, 1967 (one year to the day before his assassination) Martin Luther King Jr. gave his "Beyond Vietnam" speech. It was a speech against the use of the underprivileged and undereducated in the Vietnam war. He argued that young black men were being sent to die in Vietnam for liberties that they themselves did not have in the US.
In that speech, he famously said, "There comes a time when silence is betrayal."
Stand up for what you know is right and true.
"Simply because we were licked a hundred years before we started is no reason not to try to win"
~Atticus Finch, To Kill A Mockingbird
TKAM had a huge impact on many people, and it's become a classic book. This quote, said by Atticus before his trial, tells you not to give up even though the odds seem impossible.