I disagree with this argument – it can be illegal to participate in uncompetitive business practices while holding a monopoly position (even when those practice

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.