This is the line that really bothers me. This "misunderstood business" just annoys me a bit. There are plenty of people that have it far worse than this nutcake and don't even up like murderers. Ultimately, this is just an excuse Sephiroth uses to indulge in his vengeful and wrathful nature, just like most cliche Japanese villains of this sort do. I think they should have given him much better motivation.