The problem here is that, if you can see the adverse effects on the public, you're too late. So you need to anticipate them. That's not an easy thing to do.
It's not illegal to be a monopoly[0] (at least in the US) but abusing your monopoly is what gets you in trouble. Copyright and patents are examples of gov't granted monopolies.
[0] Fully conceding the fact that MS is a convicted monopolist and has to play by different rules than everyone else.
