A slightly bruised apple is not good, but it has some good parts. Do you think Jesus was saying there aren't any good parts in any of the world's apples?
Did Jesus qualify his statement in Mk 10:18? And besides...if any of the "apples" are partially good, then why couldn't we use the same rationale for God who alone is good? After all, you think Jesus was making a comparison between God and mankind; but in reality he was making a stark contrast! What you're trying to do is violate the Law of the Excluded Middle. There is no third option between good and evil in scripture.