Antitrust law kicks in when consumers have no choice, usually due to large barriers to switching. For example, in 1998, if you wanted to run WIN32 apps, you had

Antitrust law kicks in when consumers have no choice, usually due to large barriers to switching. For example, in 1998, if you wanted to run WIN32 apps, you had no choice but to buy from Microsoft. Note that the definition above does not mention market share. For example, Google dominates websearch market share, but competition is just a click away; if Bing or Yahoo or DDG built a better mousetrap, you could switch in an instant. Since you, as a consumer, can easily switch to a different music provider, it's hard for me to see how you can argue that YouTube is wielding monopoly power over you. And similarly, Zoe can (and does) easily distribute her music on non-YouTube platforms. Also, antitrust law is primarily about protecting consumers from harm (usually, higher prices). It's not about protecting other companies. So the core of Microsoft's antitrust defense was, "Yes, driving the price of the browser to $0 was terribly harmful to Netscape, but it was actually beneficial to consumers."