The debate has research into the sci-fi world:
http://www.syfy.com/syfywire/will-th...erson-shooters
A pretty good summary of a vast literature. Their take away point is what many have found. The games have a short lived effect on laboratory substitutes for aggressive behavior (such as honking horns at people, or giving them more hot sauce). The effects if found (debated) are very short in time. The same argument has been made for presentations of weapons (images, simulated guns) - do they make you hurt someone. Same answer.
There is a slightly different take that video games make you a better shooter and thus make the rampage killers better killers. Grossman makes this argument. It is true that we use simulators to improve performance and that's a real effect.
It also seems the case that weapons exposure influences juries (which makes some people nuts on the Internet).
These last two are different from just having a gun makes you become a killer.
There is also discussion that if you have a violent culture like in gang riddled communities, presence of guns increases the chance of violence against people who are not the gang member but related (like kids, involved women) as the distance of using a firearm makes the violence easier to commit. That can be debated as we certainly see blade related genocides and stabbings in places were gun are are to get.
That's the lecture for today.