There's ample evidence that many users aren't aware of the costs of
using NAT, or especially, weren't aware of those costs before they
started using NAT - so their choices were poorly informed. So no, it's
not reasonable to conclude that decisions to use NATs are justified by
realistic cost-benefit estimations of doing so.
NATs have been around for quite a while. This might have been
a convincing argument 5 years ago, but I don't find it very
convincing now, particularly in view of the fact that some
people who clearly understand the cost/benefits choose to use them.
NATs have been around for awhile but not everyone has been using them
for 5 years. Some of those who thought NATs were a good idea are now
looking for alternatives. For other people, NATs work just fine for
their current needs, and this has never been disputed.
Note also that cost optimization by individual users (even if
well-informed) does not necessarily produce a cost-optimized result
for
the overall community.
Of course. But then you have to describe the negative externality.
plenty of examples have already been given.
Keith