I think its a bit naive to think that even a powerful movie will motivate today's people in the same way that the "fire and brimstone" sermons did in the days before television. I even shudder to think that someone on trial for the brutal beating of an innocent will claim that he was motivated by this movie.
Mel's taking a sizable gamble here, but usually we honor the people who take the risks in our society, unless they flop spectacularly.
And, I'm sure, you'll be first in line to announce the success of this film - no? How would you define success? Box office? DVD sales? The converted?