My interpretation is a little different than what's been said so far. I think the argument is that all of what we describe as "evil" can be explained by somebody wanting something very badly, which the speaker sympathizes with ("I understand all destructive urges") and so he does not see this as evil. After all, what he wants, he wants now. He can't control himself when faced with urges, and he doesn't see himself as evil, so nobody is.
My interpretation is a little different than what's been said so far. I think the argument is that all of what we describe as "evil" can be explained by somebody wanting something very badly, which the speaker sympathizes with ("I understand all destructive urges") and so he does not see this as evil. After all, what he wants, he wants now. He can't control himself when faced with urges, and he doesn't see himself as evil, so nobody is.