Enemies know you at a much deeper level than a friend ever could. Although enemies might only know you for what you aren't. Friends know you only as much as they know themselves. Enemies and friends are both very important.
An enemy by definition is someone that is opposed to you. For an enemy to oppose to you they would have to find something to hate something that you probably try to hide. Going beyond the scope of nicetys that friends can see.
I beg the question: do you interact with your enemies a lot?
From the perspective of someone that only has some friends and doesn't really trust anyone, I feel like I can only really stand myself, so when I go looking for people to befriend I am befriending people like me. But either way you cut the cake friends... enemies... if you have them you got social motion, which a lot of people have and it becomes a hive mind where everyone is trying to take the queen.