Now that has to be one of the funniest statements I have ever read.
Some folks think that any depiction of nudity is pornography. Others believe that frank violence is just as pornographic.
And some people believe they were abducted by aliens. So? Most every home in the land has a dictionary with a perfectly good working dictionary with a perfectly good working definition of pornography. If you have trouble defining pornography, maybe you should ask the next alien that abducts you.
In the US of A, we have this concept called "freedom of press," and our courts have decided that it's quite alright to publish sexually explicit material and for adults to purchase it, as long as it does not contain sexual exploitation of children.
The same courts that decided blacks weren't real people? If we can ban pedophilia, we can ban porn. Freedom of the press is not absolute. Every freedom has reasonable boundaries.
Further, four year olds are generally not even aware of such activity and would not give that tiny DVD screen a second glance.
Some of those DVD screens are not that tiny, and four year olds aren't the only people looking in car windows. For that matter, even 45 year olds don't need that kind of distraction when traveling 80 mph on a crowded freeway.