Friendship (as the ancients saw) can be a school of virtue, but also (as they did not see) a school of vice. It is ambivalent. It makes good men better and bad men worse.
C. S. LewisIf a thing is free to be good it is also free to be bad. And free will is what has made evil possible. Why, then, did God give them free will? Because free will, though it makes evil possible, is also the only thing that makes possible any love or goodness or joy worth having.
C. S. Lewis