You apparently haven't seen the video of a fsd tesla going full speed through the fog towards a train crossing with an active train.
The cars display didn't even indicate that it thought something was in front of it, and would have happily driven right into the side of this train if the driver hadn't taken over at the last moment. (Driver was an idiot for using fsd in the fog to begin with) but it shows the cameras can't handle reduced visibility well currently, they saw the fog and just decided it was open road or clear sky.
Except the NAT device will stonewall traffic on every port except the ones I open, for my entire network, and then I can just worry about securing the software listening on those few ports, instead of having to worry about the firewalls on every device I own.
Tldr default nat behavior is a state full firewall.