People used to try to censor printed materials; now we've generally moved to censoring nudity, "foul language" and sometimes violence in audio and visual media. Already, people can photoshop tabooed types of porn. It's entirely possible that in the future virtual reality will enable us to engage in all kinds of immoral behavior. Imagine the most horribly disgusting thing people are capable of. What if they can do it in the privacy of their own home without actually harming another person? Will we allow them to do it?