Having 1 kernel thread for each CPU thread means that your program can use all available CPU threads at the same time (so you get all the parallelism available within the machine), and having a language based scheduler for each thread means you can have minimal overhead (no need to do a system call) to create a new concurrent execution (meaning lightweight/green threading similar to what python allows, except being automatically distributed by the language within all kernel/cpu threads). In Elixir this means you can create millions of processes even though the OS will only see one thread per logical cpu thread, and I never felt the limitation of this abstraction over multiprocessing (of course, Julia is definitely nowhere near as mature - and maybe never will due to stuff like preemptive scheduling and parallel garbage collection that is easier to implement in a language with only immutable types, though it seems to be moving along, and in Julia 1.7 the processes being able to move between kernel threads solving the issue mentioned in that discussion you linked).
If you want julia to use multiple system threads, why are you suggesting one not use system threads for this test? All you have to do is start julia with multiple threads and it'll use those threads for your infinite loops.
Since I didn't use dirty processes in elixir it did make me forget about this obvious issue you pointed out, that for a mutable language like Julia can happen in every thread, but that's not something that limits the expressiveness of the model, but something that requires consideration to avoid while programming and language level mechanisms to protect the thread (at the very least the ability to define timeouts that can throw an exception on any spawned process) or maybe a future framework on top of it that handles this in a safer way (something like Akka). I can only hope Julia can achieve the full potential of it's multithreading model.
