Read the Data Communications article they provided:
PIX also increases network security. Since there's no way for anyone on the Internet to know which machine on the corporate network is using a Class C address at any given time, it's impossible to establish a telnet or FTP session with any particular device.
And what about hosts that should be recognizable from the Internet, such as mail servers? These either can be directly attached to the Internet and assigned a public address or can be attached through PIX. In the latter case, the translator is config- ured to map one of the external addresses to the device not just for the duration of an application session but on a permanent basis.
At some point you're going to have to find a way to argue that the Cisco PIX was not a security device; again: it was the flagship product of the security SBU.
I was there at the time, doing IP network engineering (for a Chicagoland ISP). The PIX was a security device, and NAT was understood as a security feature (for sure, also an address depletion feature, but the argument that's being made in the post isn't merely that it was an address depletion thing, but also that it categorically wasn't a security feature, which is just obviously false.)