Why do sites have friends lists but no enemies lists?

[SuezanneCB-SuezanneC-Baskerville]

How come social sites always have friends lists but never enemies lists? Wouldn't it seem only fair and balanced to have enemy lists to even things out? Wouldn't it be kinda fun to turn on your computer and get a bunch of "So and So has put you on their enemy list, would you like to reciprocate?" If this could be tied in with an Eliza-like automatic contradiction system it would be kind of fun. Your auto-contradicter would check for comments from people on your enemy list and contradict them. Example: someone on your enemies list enters a chat room and says "Good morning." Your auto-contradicter responds "I fail to see anything particularly good about it.", or maybe, "Sure, it's good for you; you are sitting pretty at a computer on the internet blathering on about what a good morning it is, but some people are in the midst of a battlefield with shrapnel exploding around them, and that's not really so good, is it? Or did you ever stop to consider that in there are people that don't have and who will go their whole lives without ever or or I'm sure there any many other valuable uses to which enemies lists could be put on social sites.