Side Loading will be the end of secure iOS
If you think the app store keeps you safe then I have a lot of magic beans to sell you.
If anything opening up and allowing side loading would force app to stay more up on their game on security. It is surprising easy to get around app reviewer. Hell you could put something in your code that allows some deep access and massive security hole and the reviewers would never catch it. Big time if you put it on a delay function or with a remote configuration file/ feature flag. Turn it off during the review and then turn it on later. It would be installed on a multiple phones at that point and problem solved.