Back in the days when my ISP didn’t do NAT , their dsl modem didn’t block anything.
Most people do not have the capability to secure their internet connection.
I still think the op has a good point in that NAT has protected many home networks , if nothing else from ISP incompetence , even if in theory a firewall could have done it better.
Modems don't generally block anything, unless they're a modem/router combo. Have you ever actually encountered a device that had a NAT but no stateful firewall?
Back in the days when my ISP didn’t do NAT , their dsl modem didn’t block anything.
Most people do not have the capability to secure their internet connection. I still think the op has a good point in that NAT has protected many home networks , if nothing else from ISP incompetence , even if in theory a firewall could have done it better.