Historically, and today true market monopolies do not exist. The economic argument is monopolies reduce quantity and increase price; however, every company that you would call a monopoly has done the reverse. Rockefeller's Standard Oil, Microsoft, Coca-Cola, Ford, all of these companies have lowered price and increased quantity sold. You could call them a monopoly because of their huge market share, but that does not make them one by the economist's definition, nor are consumers harmed by this. State sponsored monopoly is a different thing entirely (so I assume we are excluding those), but if a company rises on its own in capitalism to dominance, then there is no problem for anyone.