[kibwen]

  > The proof of this is that several core concepts that 
  > are considered "safe" have "unsafe" portions

I don't understand this argument. Rust could have built those features (e.g. `Rc`) directly into the compiler itself and it wouldn't have made the language itself any more safe, and it wouldn't have made the safe bits of the language any more or less powerful.

In fact, `Rc` was once a first-class part of the language itself, and was indicated by the `@` sigil. The fact that it now lives in the standard library rather than the compiler is because library code is easier to audit for correctness than the compiler internals; to prove that the language is powerful enough to permit user-defined smart pointers and memory management primitives; and to permit alternative implementations of basic language features to be swapped in and out via custom standard libraries (which is way easier to do than forking the compiler).