You can't determine whenever characters on picture are consenting or not (or pretending they're not consenting but actually do). Especially if they're drawings that bear no resemblance to any real persons. So, while your suggestion is logically right by its nature, it just can't work in reality.
Well, unless laws mandate that every porn-looking picture out there must be accompanied with a signed written consent proof. But that's not really possible, too.
In your mind, would this include images/videos of cartel beheadings? Killings by religious extremists? Killings by oppressive regimes? Images/videos of the results of war? Images/videos of the results of war that your particular government is responsible for?
Torture is torture. Abuse is abuse.
I would not consider even laws with exceptions for evidence of government wrong-doing to be acceptable, as that would leave open the possibility that governments could restrict access to evidence of their wrong-doing by denying involvement in the crime, and therefore denying the public the right to distribute or possess that evidence.
We are fortunate that existing laws concerning evidence of abuse of children seemingly have not undermined our system of government. However if these laws are expanded, they will do exactly that.
^ For example, what sort of democracy would we be if the public were not permitted to see or know about the photos of abuse and sexual humiliation at Abu Ghraib (http://commons.wikimedia.org/wiki/Category:Abu_Ghraib_prison...)? If our democratic process is to be valued in the slightest, then the public must be allowed to see even the disturbing results of the policies of their nation.
Abuse of any kind, adult, child, or animal, should be investigated and prosecuted as allowed by law. The products of these acts, which could be in the hands of innumerable people for various reasons, legitimate (investigators, vigilantes, etc.) or otherwise, is something that can't be un-done, not with how the internet works.
Still, it should be important to differentiate between possession, distribution, and production in all of these cases. Any law that fails to tackle even this most fundamental concern is just plain broken, yet they get passed all the time on the emotional basis of "Think of the children!"
> Still, it should be important to differentiate between possession, distribution, and production in all of these cases.
Luckily the relevant law does what you want and answers your questions. You'll want to read it with the sentencing guidelines too.
If you're going to make a stand, at least make a principled one ("We're trying to prevent abuse") and not one on emotional basis ("Think of the children!")