2. No one would switch to Android just because of that.
3. Yes, lots of negative publicity. That's why 1. would never be reached.
Finally, one thing not mentioned: people would find a way to install the app without the app store. Every good hacker in the world would try to do it firstly, because every iphone user would be asking to be able to install Uber. And Apple doesn't want all bright minds trying to find flaws in their system for sure (I wouldn't at least)