Well, it's like this as I see it:
A lot of it comes down to the seperation between fantasy and reality. Either porn or violent fare can be really bad when dealing with an audience who takes things in a "this is real, this is how things really are" context.
Both arguements about pornography and violent games dealing with kids works from the perspective that kids are totally unable to seperate fantasy from reality. It's debatable at what age they become more capable of making such divisions. Thus my first question in debates like this tends to come down to "define 'kid' ". If your talking about very young children, then it is correct that you need to limit what you expose them to. When dealing with teens the problem is substantially less extreme. I think one of the problems with such debates is that there are problems making such divisions.
The problem with porn as I see it from the perspective of a 13 year old or so is that it tends to portray relationships in a fairly dubious light. It pretty much has attractive people using each other as pieces of meat for their own enjoyment (or more accuratly, the enjoyment of the viewer in this case). What plot or justification for the action is typically minimal, and oftentimes tacked on simply to allow for a possible defense of the movie being an "art film" if someone was to try and ban it as obscene.
The development of interpersonal skills is why I more or less have no problem with kids HAVING sex in their teens, as long as it's with other teens. I support things like distributing condoms in school, and making sex education mandatory (and not a choice left to the parents). The differance in perspective and how they view relationships, as well as unrealistic expectations that many kids might have being naive, are among the reasons why I agree with adults having sex with children remaining a crime.
I see teenage sex as part of growing up and learning about life at a slow pace with others going through the same thing. It's not something you can "protect" someone from while expecting them to learn the same lessons. As a result I kind of think something like a Ron Jeremy movie is actually more dangerous than the sex itself, and would have problem with say a couple of kids watching his movies, even if I didn't have a problem with them getting it on in the back of a car someplace (with proper protection, which is why I support mandatory sex ed, and making such things availible).
When it comes to violent games, again the games are rated for a reason. In general I think most TEENS are capable of differentiating between fantasy and reality to the point where it isn't a big deal. For all of the excuses made about games causing violence (including kids using it in their own defenses to get reduced penelties after crimes) I feel that people have always been violent and most of the situations that end in violence would have ended that way irregardless of whether such games were being played. It's not like society, even school, was a peaceful utopia before the "evil" of video games. To be honest people have been blaming everything from rock music to comics for the violent and sexual "animal" behavior of kids since the dawn of time. The current generation of adults always looks down on the current generation of kids who are doing exactly what they did, and say "oh gee, we weren't that bad" and blaming whatever is relatively new to that generation for the problems.
I find it oddly ironic when you have people talking about how video games cause violence, and how horrible some of these issues of school violence are, yet variations on the whole "Dangerous Minds" theme of some teacher "reaching" a group of roughneck teens is ancient. As are "nostolgia" movies with like greasers and jocks and other cliques having massive gang fights and "rumbles". Not to mention the whole street race motif with kids racing cars towards cliffs and such, or playing chicken. Oh yeah the whole "Baby Boomer" and before teen stereotypes they left behind and worship just showed how much more passive things were *sarcasm*. The movies aren't entirely accurate but the grain of truth there is the point, as well as why they hit the nostolgia buttons. In fact if you dig through old papers and such you'll find a lot of wild things happened decades ago. Things like "Columbine" just seem so "amazing" because the media is powerful enough where what would have been a local issue and covered up was able to be distributed to the entire country, in real time, as well as being sensationalized by the way the mass media works, and things like the Blogosphere where any goofus can share his opinion with millions. Enough people saying the obvious "OMG is horrible" and a really bad situation, can be escalated into something akin to a national crisis. 30-50 years ago a couple of really big groups of students could have gone at it for the stupidist of reasons and seen as many deaths, and it wouldn't have gone beyond a local level. Trust me, people didn't write books like "Rumblefish" and see them turned into classics because they were seen as trite and meaningless fantasy.
Simply put, humans are violent. Teenagers are wild. This reality has always existed, and will always exist as long as our species does. Video games didn't cause this. If anything I think they help a lot of people vent impulses and burn off excess mental energy in a way. Not in the sense of some nerd trying to sound "big" saying "oh yeah, if it wasn't for games I'd be out there killing people" (trying to act like he's protecting all the people who pick on him by playing video games... oh how noble) but in a very general and healthy sense.
What's more if violent video games were ever done away with, kids would just find something else, and since games seem about as harmless as it can get (overall) chances are whatever they wound up doing with that excess energy would be worse.