Darkness cannot drive out darkness; only light can do that. Hate cannot drive out hate; only love can do that. Hate multiplies hate, violence multiplies violence, and toughness multiplies toughness in a descending spiral of destruction....
The chain reaction of evil - hate begetting hate, wars producing more wars - must be broken, or we shall be plunged into the dark abyss of annihilation.
- Martin Luther King Jr.
as quoted on God's Politics.
http://www.beliefnet.com/blogs/godspolitics/2006/12/voice-of-day-martin-luther-king-jr.html
