Sexual arousal begets sexual gratification. This is where the bad things start. This is the point where crimes of passion are committed: adultery, rape, sexual harassment, incest. These crimes are what alarmed the authorities and triggered the banning of the said materials.
Banning pornography is a noble idea, however, not a very practical one. First of all, sex is a part of human nature. Even if pornography no longer abounds, fact would remain that humans are sexual beings by nature. They would keep finding ways to satisfy their sexual needs, whether directly through intercourse or partially through pornography. For as long as humans have sexual drive, sex crimes would never cease.
Another thing that makes the banning of pornography not practical is the media. Nowadays in this modern world, there are myriad ways of passing along information. There's the Internet, TV, cellphones, mobile players and other such media that could easily transmit all sorts of data from one to another. Such gadgets are vulnerable to the clutches of pornography. How many cellphones today don't have at least one sexually explicit content media content? How many exhibitionists flaunt their wares through the Internet via webcams? These may seem like small things, often overlooked as individual perversions, but these are also forms of pornography. So even if the authorities somehow manage to eliminate porn videos and magazines, technology still provides ways for pornography to flourish.
Banning or condoning pornography has minimal effect in its power...