I'm not sure it's reasonable to use the monopoly argument at arbitrary level of granularity. For instance, while Apple has a monopoly on iOS app by definition, Ford also has a monopoly on Ford cars. Monopolies are only a problem when there is no viable competition. In this case, the competition is Android et al. By saying you only want an iPhone, you are restricting your own choice. That said, it's perfectly fine to complain about the policies Apple implements. Complaints are part of the free market process, and in many cases bring about change for the better.