NAT grew out of need. It didn't grow up in the IETF. We did have a NAT WG, to document, define common terminology and guidelines. We took a lot of heat for just documenting what was out there. The marketplace resulted in the success of NAT. Even if there had been limitless address space, it's unlikely NAT would have been avoided.
nat is not a technology, it is the anti-$deity, at least to some. the ivtf loves to throw out multiple confusing and competing technologies and say "let the market decide." but it somehow has had very deaf ears when the market decided nat in a very big way. this is not to say i would want a nat to marry my brother! but, ome months back, some wiser heads in the ivtf listened and agreed that nat-pt (no, alain, i will not be silly and let people force me to confuse things by calling it something else), is seriously required even though it is disgusting to us all. thank you russ and jari; and i am sure others will climb on the bandwagon and wave flags. the alternatives are more disgusting, and lack of nat-pt is a serious impediment to ipv6 deployment, a critical one in a world of ipv4 address space scarcity. for an example of the problems of public proxies, as Jeffrey Streifling said (in http://www.civil-tongue.net/clusterf/ wiki), o Email/SMTP is a mandatory application o Everyone needs to be able to send email to arbitrary recipients, i.e. everyone else o But, due to SPAM, no one can run an open SMTP relay o So all IPv6 sites need to have the ability to SMTP to arbitrary IPv4 sites o Therefore everyone needs private dual stack relay until the world is all dual stack SMTP randy