I would never debate NAT was marketed as security (as marketing is often detached from the reality of what's being sold) but I'd be interested why it's a material factor in securing networks independent of the stateful firewall mentioned, which most seem to actually rely on. The "snooty" people probably mean less what may have been marketed to consumers and more what the standards which introduced it say. E.g. https://www.rfc-editor.org/rfc/rfc1631 notes address depletion and scaling as drivers in the opening but the only mentions of security are later on in how NAT actually makes security more difficult.

I.e. it would seem whatever argument could be made about security from NAT, poor or not, intended to be security or not, would be immaterial in context of stateful session tracking with outbound originate allowed alone w/o doing the NAT on top anyways.