Google and Facebook are pushing IPv6 primarily because those companies attract nerds who understand the problem. IPv4 NAT does provide some degree of privacy,

Google and Facebook are pushing IPv6 primarily because those companies attract nerds who understand the problem. IPv4 NAT does provide some degree of privacy, but law enforcement can still identify you if the TCP source port is logged. Is this incremental privacy benefit really worth hampering the growth of the internet forever? The goal of IP is to route packets from A to B, which fundamentally requires knowing the locations of A and B. Privacy and efficiency are contradictory goals, and it's much easier to build privacy on top of an efficient network (e.g. using proxies and VPNs) than the other way around.