This just in: would-be monopolist things monopolies are just fine.

If you are wondering why they are a problem, you might read "The Jungle", or any history of the era of the big industrial trusts. Or you could read "When Wizards Stay Up Late", a history of the Internet's invention. AT&T, the communications monopoly at the time, was a big barrier to the development and growth of the Internet. And, from their perspective, rightly so: they made a zillion dollars from charging for voice calls, something everybody now expects to be free.