It's an absurd argument. If you want to only install app store apps, then only install apps from the store. That's still possible you know, even if other people aren't forced to. That's why these arguments always boil down to bullshit about how you will be "forced" to use Facebook from outside the store and that would be terrible because being on Facebook on an iPhone is a human right or something.

If you like Apple telling you what to do, fine. Choose only from their menu.