Stacy Tibbets has a good point about how voice grows out of conflict. He's thinking in the larger cultural context--about how strong voice of new journalism emerges when there's no longer a moral and cultural consensus: people can no longer write "for everyone" in "our voice"--where it can all be taken for granted. Perhaps that explains why academic discourse is breaking down now: it used to be possible to speak for a consensus: we all agree on who we are and how we talk. Now that's no longer true--and so voices have to define themselves; and there are stronger flavors of voice.
But the same thing is true on the individual level: and this is a good antidote to my "safety" emphasis. I guess we need safety for our voices to come out (and Bakhtin agrees); but "voices get raised" when there's a fight. People speak out strongly when they are mad or disagree or have to fight to establish themselves. It may be that one of the main things we need to help us make and find powerful voices for ourselves is situations of conflict and disagreement. We need just enough not to shut us down.