Yes, they do get their own virtual address space, but any process running as your user can manipulate any file that user has access to (by default, without any

Yes, they do get their own virtual address space, but any process running as your user can manipulate any file that user has access to (by default, without any sandboxing, which some recent apps on macOS/Linux do use, but which is not the default). Often any process running as a user can attach a debugger to any other process running as that user, which is tantamount to having complete control of that process (because a debugger can read and write memory).