[Crito]

I do not believe that mathieuh considers Mandela's "not always nonviolent" stance to be a negative.

I think the idea is more along the lines of "violence had its place in that conflict, it was for a good cause, and it worked."

Injecting my own opinion here: I think that if we forget the usefulness of violence then we may risk failing to repeat Mandela's success, should the need ever arise. Nonviolence is great, but only when it works. When it doesn't, violence should be embraced. We should embrace whatever is necessary to get the job done, nonviolence should be seen as a (typically very effective) means to an end, not an end in itself.