Earlier quoted context omitted.
How much of a fee do you think you should pay to install applications on your computer? The same amount as that. Or provide alternative ways to install software. This is a problem of their own creation.
As soon as you open the door to side-loading, you'll have scammers and data-siphoners force all their users to side-load so that they can completely bypass Apple's privacy controls and security features. The entire iOS ecosystem is built on the App Store review process as a gatekeeper for entitlements and the capabilities they grant (through API access). How do you solve that problem for side-loaded apps?
They do not review source code. There is malware on the Apple app store, because they do not review apps for malware. Because they do not review source code.
Any other opinion is just not true.