In the past, the heroes of movie and television shows were usually people who strictly followed the law. Now, heroes are often people who take the law into their own hands, who see an injustice or evil and seek to rectify it personally, sometimes brutally, regardless of the consequences. Such portrayals signal, to a child, society's approval of that behavior. Lacking the judgment that comes with age, a child who feels he has been dealt with unfairly may copy that behavior, with disastrous consequences.
John Stuart Mill on free expression: "The sole end for which mankind is warranted, individually or collectively, in interfering with the liberty of any of their number is self protection." Free expression is a wonderful thing, in principle. It is the foundation of a democratic society and many of the principles that modern society is based upon. Unfortunately, there is also a darker side: the detriment certain kinds of expression can have on children's development. The same children that will one day be the teachers, politicians and businesspersons of the world. If they are allowed to be exposed to less than the best in their formative years, the results might be a society without morals, children without moral fiber or integrity, mentally scarred by the horrors they have been exposed to. An eight year-old boy and a ten year-old accomplice now face charges of rape and sexual molestation after forcing another student to have sex with the eight-year old. Both told police that they had learned about sex from a pornographic video that the eight year-old's father had rented. The eight year-old told police after watching the tape that 'I wanted to have sex with her.' Pornography is just one of the forms of expression taken too far and is detrimental to the children of America.
Here's an interesting study that was done many years ago to make a point. I'll set it up, then you guess what happened.