Every time a user space program makes an syscall the OS already has to go through layers of indirection. The OS can provide a program with a virtual or restrict

Every time a user space program makes an syscall the OS already has to go through layers of indirection. The OS can provide a program with a virtual or restricted view of the filesystem instead of the real thing just as easily. The OS already prevents processes from accessing each other's memory. There are some difficulties with sandboxing peripherals and GPU access, but for the most part sandboxing has absolutely no performance impact. Sandboxing doesn't mean the OS has to spin up a virtual machine every time you want to run a program.