[Quarrelsome]

well to put it another way; in the time that I have lived violent video games have exploded in popularity and violent crime has apparently decreased substantially. That's not to say there's causality between the two but it would definitely support the premise that violent video games at least don't encourage violent crime.

[Natanael_L]

I also don't think there's a strong correlation / causation, but this isn't solid proof.

If there was a causation then the reduction in violent crime could be muted by a small factor due to games, while the net decrease is (as before) caused by an even larger independent factor. In other words, the net decrease could have been larger without the presence of games.

What it does instead show is a maximum plausible effect size, and that it likely isn't worse than the activities which it is replacing.