Modern OSes are designed to prevent users from attacking other users (or the system) with malicious code. They are not designed to protect the user from malicious code they themselves install.

> We do have something like that. It's called a web browser. A browser is a small VM that runs utterly untrusted code relatively safely. In many cases it's code from the sketchiest ad networks and other hellholes imaginable.

Given how many issues there are with ad tracking, fingerprinting, and other privacy related issues, I don't feel the web browser is particularly safer than an iOS app. What can an iOS app really do that a browser app cannot at this point?