The problem with these monopolies is the same as with others : they capture excess money, which hinders innovation in the long run.
Hint : I don't believe in the free-market la la land BS anyway.
Once upon a time, Altavista was The Search and MySpace was The Social Network.
It was illegal for some reason, you know.
> Once upon a time, Altavista was The Search and MySpace was The Social Network.
They never quite reached the monopoly level, though.
Secondly, it's kind of silly to think about web monopolies when users can freely change operators. Google, Facebook etc have to work hard to maintain their users.
Actually you're wrong; it was made illegal because most people in command back then thought that it made more sense. See http://en.wikipedia.org/wiki/Natural_monopoly.
Free-market religion is relatively new, and remains largely questionable.