The main problem is that somewhere some database will hold the information about citizens and a "likesPorn" flag. That information is personal. Alcohol and cigarettes both have age limits, but there is no database that people need to register into ("wantsBooz = TRUE") before being able to purchase their first drink.
The adolescents teaching each other how to get around filters - that is exactly what ends up happening. A few years back, Turkey had a pretty long ban on Youtube. Countless sites for tweaking browser settings specifically geared for Turkish Youtubers emerged. There was even a cartoon by a prominent artist that depicted the PM declaring his agenda: "We won't lift the ban until we have 70 million DNS experts."
But yes, this apprehension of nudity is something I've always found so bizarre. Why is seeing skin of our species such a big deal? At what point of our social evolution did it evolve that way (because the idea of clothing is pretty universal to humans).