This was a very controversial move that Jeff Schiller had the foresight to drive through. There are still arguments about it, but overall it was a "good thing". .pm John Young writes:
Excerpt on Net security from "Upgrading the Internet," a roundtable discussion of the Internet Society on the next generation of Internet protocols, IP Version 6.
Discussants: Vinton Cerf, Stephen Deering, Christian Huitema, Haruhisa Ishida, Larry Landweber, Eric Schmidt, Lixia Zhang.
A most important aspect of the IPv6 is the somewhat controversial decision to require that all v6 implementations support strong privacy and strong authentication. At this level, all of the security problems won't be solved, but we can authenticate and maintain privacy of packets that flow from one machine to another. This will eliminate many security threats in the current Internet, such as source-address-spoofing, source-related routing attacks, password sniffing, connection hijacking, and so on.