What would you recommend that doesn’t have a GC? Zig? C? Rust is a fine choice. Besides if you really don’t care, just make the entire program unsafe and you’ll still reap benefits over C or C++.
Whatever language and toolset gets the job done with the least amount of effort. Given the hoops that Discourse had to jump through to get Rust working, that wasn't a good technical decision. They'd have got the same result with less pain with C++.