1. Users have perfect choice in which apps they install.
2. Developers will release their apps on all available app stores.
But many users are compelled to install apps that they would prefer not to and it's not at all obvious that developers would support two app stores instead of one given the choice. The net result of that combination is that some (many?) people would be compelled to use both app stores against their inclination.
The only wrong part is users not being in control over what they can install on their devices and from where they will install them.
Yes, it is possible that people will be forced to install applications they do not want, but this isn't something that is or even should be up to the OS vendor to try and protect against - the person being forced to do that is the one who should and if they cannot, then legal action should be seeked. The entire issue is outside the scope of the OS.
You can argue (as I think you are) that those losses are outweighed by the gains of a more open ecosystem, but to many users they are meaningful losses.
Others, in the meanwhile, should be able to install whatever application they want if they want to do that. Just because the current situation aligns with what you want to do doesn't mean that it is the perfect situation for everyone - but as long as your situation isn't affected (assuming what you want is about you and not about forcing everyone else to be like you) then you should be fine.