This "scientific" debate is quite similar to the one about global warming. One group will use any study to prove their (politically or financially motivated) point, and the other will use any suitable study, to disprove it. If any one group appears to have the truth on their side, the other will attempt to seed confusion and attempt to create their own evidence by funding friendly research groups. It's all throwing mud really.
And if you follow such a debate, it's usually easy to see what the motivation of each of the factions is, and which one is more likely to be right.
The sad thing is, this scientific mud throwing will last as long as the
political/financial motivation is present.
Other good examples are the scientific debate about "intelligent design", and earlier TV, and movies and violence, the health effects of tobacco, the effects of some drugs (mainly the farmaceutical's cash cows..).
The good thing is, that sometimes there are metastudies, studies that benchmark and compare all previous scientific studies, and form an opinion based on that. I'm not aware of any such study regarding the effects of videogames.