One only has to ask themself, why don't they allow their young grandchildren to watch p 0 r n or extreme violence. Do you not understand that at any age a spirit of p 0 r n or violence can embed itself within our minds? Do you not see people addicted? I'm not saying all are, but it can happen. Why take the chance of crossing that line where you have tested God and He allows satan to have his way with you in order for you to learn?
Personally I like my life less tested in areas like that. But to each his own. p 0 r n has been known to cause much mental infidelity within a family, as well as physical infidelity. People innocently think it will enrich their marriage bed, when in fact it causes it to be defiled by the images of other lovers dancing around in their minds. If you don't have that problem then perhaps you haven't crossed that line as of yet. I just don't like to play with things like that. There are many other games people can play. It is however, a personal choice for all.