That's quite a ridiculous statement in this context. Even highly-trained, extremely smart developers are proven to not be able to use C without introducing gaping security holes. That's not "it can hurt you". That's "it hurts you and everyone that is exposed to your RCE machine".
Redis has RCE exploits which would not exist in a memory safe language [1]. QMail had an RCE as well[2] and DJBDNS has had a security bug which would not have occurred in a memory safe languages [3]. The linux kernel has had an incredible amount of memory bugs over the years. The software you mentioned does much, much better then the average C written code. But it still has had issues with memory. So in fact all your examples prove my point.
C is not C++. There is a reason core services for DHCP, DNS, etc are built in C and not Rust. If you're a careless developer you can have security vulnerabilities in any language.
That's only true on Linux and other systems where the kernel has been written in C. On some platforms the kernel provides no backwards compatibility guarantees and that means backwards compatibility is handled by libc. This means C is enshrined into the platform and often the path of least resistance.
There was also a pure Rust Wayland binding that failed because Wayland assumes that you are using C semantics which made it hard to provide a safe interface for Rust that was also convenient.
