Also makes good designs hard to write, designs that can be significantly more efficient.
Passing messages is not a universal solution to shared mutable state. It is great for certain patterns but suboptimal for others.
For example you can just write a lockless triple buffer for efficient memory sharing and wrap the unsafe usage of pointers with a safe API. now you only need to pay attention to those specific unsafe calls.
It encourages good designs but it does not make them easy to write, but that's somewhat the point. Its not trivial to design a safe API that pushes performance limits.
> just write a lockless triple buffer for efficient memory sharing and wrap the unsafe usage of pointers with a safe API
This isn't practical or pragmatic.
And I say this as someone who likes rust and develops in it every day.