But those hacks wouldn't provide the same guarantees that language-level changes provide. Sure, you can try not to impact other thread's heaps, but nothing is stopping me, which means a simple programming error has the potential to impact multiple threads. As a result, you can't just "reboot" that thread (a critical piece of what makes Erlang interesting), because you have no guarantees its errors didn't impact other threads. You also have no guarantees that the underlying libraries aren't mucking up all of your carefully crafted memory management.
It's like the kernel protecting memory so applications can't overwrite each other. Sure, applications could just write to their own memory, but nobody actually trusts that model[1]. Instead, they want something below that level enforcing good behavior.
1. Obviously, virtual memory adds a wrinkle to this that kind of forces kernel protection, but even if we had literally unlimited RAM, we would still implement kernel protections on memory.
It's like the kernel protecting memory so applications can't overwrite each other. Sure, applications could just write to their own memory, but nobody actually trusts that model[1]. Instead, they want something below that level enforcing good behavior.
1. Obviously, virtual memory adds a wrinkle to this that kind of forces kernel protection, but even if we had literally unlimited RAM, we would still implement kernel protections on memory.