Capitalism does facilitate monopolies or industries with razor thin margins like airlines. However, the space of competition is a revolving door with constant opportunity to create something better (that people want) than the established players or to enter a new arena entirely. Ultimately, since consumers are the choosers, it works in their favor. It was the consumers that wanted these companies to exist, and the profits are a proof of that.

However, sometimes there are unpriced externalities like the competitive advantage of removing your own manufacturing waste by dumping it into a stream. That is where governance (whether self or the state) comes in.