The basic argument is, it's a cell phone. It's an embedded device. It's not a computer (as proved by the "post-PC-world" phrase). A traditional cell phone could run apps (Tetris, Snake, etc). A game console is built to run "apps" (video games). Yet no one is loudly complaining that they cannot run their own software there for free. A smartphone is more closely related to a game console than a traditional personal computer.
Will we reach the point where smartphone (or smartphone like devices in the future) are considered computers and we can use them freely? I hope so. It might happen. It might not. What we can count on is there will always be the choice on the market for those who require that choice. Not everyone does. I have a Windows Phone. I've never been bothered by not being able to install my own software. I also have an HP Touchpad with Android and WebOS, the two freest OSes on the market right now. Never sideloaded. I don't need to.
My point? Your outrage is misplaced, for several reasons listed above. People often talk about consumer choice, but the rubber meets the road when consumers willingly make an informed decision (in my case) that the crowd doesn't understand. I bought a Palm Pre not because of the freedom, but because of the UX. I bought a Windows Phone for the same reason. Sometimes a smartphone is just a smartphone. You might not understand my choice, but I do and that's what counts in the end.