Google Play has already proven that wrong.Except nobody realizes that when the app developers realize they can sideload to save the percentage fee, they will pull it from the App Store and force us to sideload. Leaving the App Store as barren as the Mac App Store.
You can sideload on Android, yet developers still use Google Play store to distribute their apps as it is a trusted installation source.
Sideloading on Android is also no longer a system wide option. You have to designate which apps are allowed to install from unknown sources. Never allow your browser to be one of those sources and you'd be safe from drive-by malware installations.