Okay, this is where the analogy breaks down: one can totally have a
non exclusive app store where people are guaranteed a certain level of quality, and a reasonable expectation of not downloading malware. For instance: Steam.
The only thing non-exclusive stores can't do is protect people from themselves. And even then you could still have the kid gloves on by default, yet let people take them off whenever they want. For instance by displaying some mildly scary warning about some program not being verified by the OS vendor, and then still let people click on the "install anyway" button. (The "Windows protected your PC" popup would be like that, though I think it overshoots to the point of dishonesty.)
