Fair market competition is not possible if one actor is in a monopoly position. And I am curious to read what economic theory says about competition over a fre

Fair market competition is not possible if one actor is in a monopoly position. And I am curious to read what economic theory says about competition over a free product. I mean, I understand their revenues come from advertisers, but they are trying to get users, for free, like if it were a market competition. I wonder how much this model holds water in that case.