alt Hacker NewsNAT is not a security device. A firewall, which will be part of any sane router's NAT implementation, is a security device. NAT is not a firewall, but is often part of one.
Any sane router also uses a firewall for IPv6. A correctly configured router will deny inbound traffic for both v4 and v6. You are not less secure on IPv6.
Misconfigured firewall is a gaping hole. Misconfigured NAT is not letting data from outside into your local network.
So firewall is actually worse than NAT.