Being allowed to mutate an integer (or object) through two different pointers on the same thread is perfectly safe and even useful (in the general case, for non-tree-shaped problems) on a CPU. Rust adds unpleasant syntax to achieve it through Cell, unpleasant syntax and undefined behavior footguns to do it through raw pointers, and guaranteed undefined behavior to do it through aliasing &mut, so I no longer treat Rust as a general-purpose programming language. And when teaching beginners, this would give the incorrect impression that it's somehow undefined behavior to access memory through multiple pointers on the same thread (rather than merely a tradeoff which increases code flexibility at the cost of local reasoning).

And on a more personal level, I dislike the Rust community (and language, eg. for loops depend on trait resolution)'s heavy use of functional, generic, and higher-order function abstractions (rather than explicit imperative code amenable to sequential reasoning). I feel heavy use of generics is confusing in a language used to teach programming to students (and I think usefully learning mainstream programming revolves around algorithmic reasoning from the level of memory and bytes through structured programming, rather than pure functions and iterator combinators).