Diversity in approaches strengthens nonviolent campaigns, as documented by Chenoweth and Stephan (2008, 2011).
This does not extend to a so-called diversity of tactics that includes violence. A small amount of violence can derail a campaign quickly and closes off many of the paths nonviolence can open. Nonviolence does not limit the diversity of tactics. Since Gene Sharp named the first 198 in 1973 the number discovered or invented around the world has probably at least doubled. That is a long list of tactical options open to use and to creative prompting toward additional new tactics. The diversity is expanded when a movement uses nonviolence to create additional space in which to organize, recruit, and affect public policy--and to create more tactics that violence would shut down. This is evident in many newer campaigns that refuse to remain stuck in the models we often used in the 1980s, patterning ourselves after the Civil Rights movement (1955-1965). These new movements, ramping up in Serbia in 2000 and extending eventually into Arab Spring and now the extant Occupy campaigns, are demonstrating great creativity in some locales and engaging in much more rapid learning via instant communication.
Still, there is one nearly monotheistic underlying value that can undergird all these new ones, even as they explore and expand, and that is nonviolence. Gandhi called it the first article of his faith and the last article of his creed, and he also described his life as "experiments in truth." In my opinion, Gandhi would be quite excited about all the improvements to his methods that have piled on since 1955. If he were alive, in my town of Portland, Oregon, and healthy at a mere 142 years of age, he'd be camped out now with Occupy Portland and happy. He'd be thrilled about the pace of learning, the focus on training, and the willingness to adapt, heal, challenge and evolve that I witness there, I think.
So, yes, Nonviolence is nearly a religion for some of us and certainly is a faith-based idea when heading into a confrontation with heavily armed police or military members. I've done both many times and trust me, faith is necessary in those moments. The faith is based not on dogma from a sacred text, but on equal parts knowledge that the stuff has worked and that, at the very least, we are not adding to the violence in this poor world when we take the field toward peace and justice. I don't worship nonviolence, but I place my informed faith in it and welcome empirical examination of all approaches. So far, those explorations bear out my experientially informed faith. Nonviolence is the biggest tent of all, encompasses the most diversity, and is the ultimate inclusive method with a thousand strands.