The legality is not very interesting imo. Monopoly law has been absolutely gutted by Reagan, and weakened by every single (yes, every single) administration since.

The question of whether having a monopoly position and not abusing it is something we as a society should do something about is, to me, equivalent to the following. If someone owns an automatic rifle, but isn’t shooting or threatening anyone yet (i.e., using it to harm society), should we do something about it? What about a bazooka? More abstractly: should society aim to prevent harm when reasonably possible, or only punish it after the harm is already done?

An earned monopoly is still a monopoly. Anyone who feels that the power that Steam wields in the gaming market is not an issue, I urge you to think or learn about why monopolies are harmful – not in relation to steam. Think about a manufacturer of gizmos completely cornering the gizmo market and what that would mean for the people wanting to buy gizmos, as time passes. Don’t think in terms of the laws or definitions of some specific country, just think about the effect it would have on society. Worst case scenario you lose some time and gain some insight on monopolies