[rlucas]

No, it can be against the law merely to have (and keep) a monopoly.

It is against the law to acquire, or to perpetuate, a monopoly by any combination or conspiracy in restraint of trade.

Although you're quite right that the move into the browser market was a big part of the case against Microsoft, there were other pieces to that case. There was a whole bunch of work around APIs/ABIs and in particular, denying other parties access to secret or privileged APIs in order to cripple potential challengers to the existing OS market (e.g. Java/Sun).

(Notwithstanding that the Microsoft strategic work around the browser stuff was a very correct reading that the browser was destined to become the de facto OS.)

Yes, it's complicated and there's a whole century+ of interesting jurisprudence. But it's not sufficient to just declare it's OK to have a monopoly -- you can be at risk of antitrust suits even just 1. having a de facto monopoly and 2. doing the "normal" smart business things to hang onto it.

For further reading, start with https://www.justice.gov/atr/us-v-microsoft-courts-findings-f...

[matthewmacleod]

I disagree with this argument – it can be illegal to participate in uncompetitive business practices while holding a monopoly position (even when those practices would be competitive in another market) but that does not make it illegal to have a monopoly position. The parent is right - having a monopoly position in a market is not illegal.