One of the many theses I'd like to write is the effect of such
regulations on the market and mores of a society. I'll hold off on the
morality issue (basically, laws on obscenity tend to lead to odd fetishes
which the lawmakers may find more alarming than what they were trying to
prevent (look at pubic hair in Japan)) and state that I think one reason we
do not see protest from the adult community from such measures is that it is
a barrier to access for their market. If you have to give a credit card to
see their stuff, you've essentially knocked all the amateur and freebie
nudie sites they would otherwise be competing with. I'd love to do a case
study followed with some analysis of lost consumer surplus, gained porn site
surplus and global inefficiency.