The whole discussion is confused from the start. When people talk about the "security of NAT" they are not talking about NAT at all, but about what happens when NAT is misconfigured or switched off. In the case of IPv4 it means nothing works and your computer isn't reachable. The system is fail safe.

Meanwhile with IPv6 it's the other way around, everything is wide open unless you have a working and properly configured firewall.