Here is a nice game about concurrency. It should answer your question why it should be feared by understanding how it works: https://deadlockempire.github.io/

As of my understanding it is fearless in Rust, because the problems that might came up are solved on language level or the compiler warns you about them. (I have never coded Rust, I just deduced this from the comments)

Rust ensures that while one thread is accessing a datastructure that no other thread will modify it. It does this by only allowing you to have either one mutable or multiple readonly references to a datastructure. Code marked unsafe could violate this, which is why it should be rare and well reviewed.

https://blog.rust-lang.org/2015/04/10/Fearless-Concurrency.h... Is from just before 1.0, and so is slightly dated in some ways (scoped threads are in a package, not in std) but should give you some explanation.

Have you followed any of the links?