Pelosi correctly points out that violence should be punished, regardless.  Any one who opposes the white nationalists and their ilk at demonstrations like Charlottesville expect that they will wind up on the right side of history.  But that favorable judgement will not follow their high ideals if violence is met with violence.  
Gandhi, King and their followers who committed to the moral strength and true bravery of pacifism realized their goals by showing the world the truly despicable nature of those they opposed by their willingness to accept physical punishment in pursuit of the higher goal.  If the white nationalists gain too much traction within our country, with the wink and nod from Trump, then it will  most likely require the bravery of non-violent actions like the Civil Rights movement from the 50s and 60s or an all out war like the 40s.