You have bazillion types of generic computers to choose from. People pay huge overhead to apple exactly because apple makes choices for them - regarding what settings are reasonable to have, what software they want you to use etc.
Personally I don't understand monopoly arguments. If we are talking about some ISP, something like Nestle or even social network/apps, I can somewhat understand it. But here? Users are people who bought Apple hardware to use it based on rules set up by Apple.
I'm not much fan of Apple, I sincerely want to understand the monopoly argument. It seems to me as if people would want to split BMW because .. I don't know we want to be able to install our own custom AC. Because maintenance of the stock one is too expensive.