It's not, because in the real world NAT only affects your outbound connections. That means that turning it off only changes the behavior of outbound connections, not inbound ones.
Any inbound connection that would have worked before you turned it off will still work afterwards, and any that wouldn't have worked before will still not work afterwards.
Any inbound connection that would have worked before you turned it off will still work afterwards, and any that wouldn't have worked before will still not work afterwards.