As I recall, it wasn't just that unsafe was being used, plenty of libraries use unsafe, but that there were multiple examples of unsafe being used with provable

As I recall, it wasn't just that unsafe was being used, plenty of libraries use unsafe, but that there were multiple examples of unsafe being used with provable soundness issues when it was possible to do the same with safe code and no performance loss. On a web server which the author was advertising as production ready. Additionally the author was reluctant, and in the final case outright refused, to accept fixes because they weren't interesting. For that last one, the fix was to replace the custom Cell (or RefCell, I forget) implementation with the one from the standard library. The big "dog pile" happened on that last one.