If you are going to invoke “antitrust laws” to whip out “you’re wrong”, you should make sure you know what you are talking about.

First, let’s assume we are taking about the USA to make this manageable.

Let’s start with a baseline: monopolies are not illegal. Let’s say that again: monopolies are not illegal. If that is your point, “you’re wrong”.

There are many legal monopolies. The government even runs or “licenses” some of them. The US postal service comes to mind.

Second, let’s define monopoly. The word literally means “single seller”. It is only accurate to use it when consumers only have a single choice or where their choices are so constrained that (as a grouo) they effectively have only one viable choice.

Legally, a monopoly is not really an expression of market share but of market power. When we are effectively forced to buy from “one seller”, there is an illegal monopoly.

So, before go further, let’s acknowledge that Valve has competition. Consumers are not “forced” to buy from Valve. They “choose” to buy from Valve as a “preference”. Very, very different.

Now to antitrust laws. Antitrust means anticompetitive practice. This is what the law actually cares about. These laws are intended to prevent “abuse of power” that protects a monopoly from completion. That is what makes a monopoly (legal by default) an “illegal monopoly”.

In fact, the law does not define “monopoly” at all but rather “monopolization”. Monopolization exists when an entity acts to ensure that there are no viable substitutes available that the consumer can choose instead.

If you want to invoke “antitrust laws”, you have to expose the anticompetitive practice and illegal “monopolization” activity. You have not done that. The fact that Valve is winning in the market is not enough for you to dismiss everybody else as wrong.

I am “pretty sure” that the “pretty sure” guy is correct. What does that make you?