Has nothing to do with monopolies, having the market slowly condense into one mega company does not create competition and results in higher prices for the consumer.

You don't have to have an absolute monopoly. Microsoft was punished for anti-competitive actions in the 90s when it bundled its Internet Explorer browser into Windows.

Even though other browsers existed, like Netscape Navigator etc, Microsoft was still found guilty of violating the Sherman Anti-Trust Act and guilty of anti-competitive action, both in the US and elsewhere.

Microsoft was forced to create a version of Windows without IE bundled, and other corrective actions.

A duopoly isn't great, either.