>I briefly Googled Patrick Galbraith, and he does not appear to have the relevant education in psychology necessary to conduct such research, so I would strongly prefer medically-authoritative sources of information.

I'm not talking about the psychological point of view, I'm talking about the cultural anthropological point of view. For the psychological point of view, you're better off looking at the effects of porn on its consumers, and to what extent its consumers export the beliefs. As far as I know, it's a small proportion, and not the typical consumer. See Hald and Malamuth's work for that. Also see work on fiction-communities, such as studies on fanfiction users. These also tend to be cultural-anthropological point of views. I am not aware of any empirical psychological study on the intersection between fiction (2D or 1D, that is) porn and pedophilia. Taylor & Kohut note that porn effects research is a shaky science with a variety of methodological flaws. Studies on pedophiles are even more unreliable, since they mostly concern those who have either (i) already abused a child or (ii) already been found in possession of real child pornography. See a chapter in Gary Young's book, The Gamer's Dilemma for a depth-discussion of the empirical status of a hypothetical link between virtual CP and pedophilia.

I don't have a link on hand, but Galbraith's article in Image and Narrative entitled "Lolicon: The reality of 'virtual child pornography in Japan" is a study of the phenomenon and its fans. His doctoral thesis also includes fieldwork in Japan with fan communities.

As far as I know, there is no empirical psychological study which confirms or denies that the majority of these fans are pedophiles, or that they feel the same way about 3D children as they do about 2D children. The best resources we have are twofold: how do people understand fiction? And how do fiction-oriented communities guard interpretations of fiction? Galbraith sets out to provide answers to these questions.

>I have absolutely no reason to believe that people who are sexually excited by the concept of children are limited to drawings of them

I don't think you have reason to believe the converse, either; at least Galbraith's work provides a hint (even if a weak one) against your conclusion. You may also have reason to believe based on how BDSM practitioners and enjoyers interact with their own pornography; for instance, how it has been studied that women with rape kinks do not themselves wish to be raped in real life, or how most people navigate pornography, in particular heinous or non-consensual acts. Incest pornography and furry pornography are interesting points to consider here. We also have some orthogonal evidence from video games and lasting aggressive attitudes outside lab settings - as far as I know, consistently fail to show persistence. Additionally, the rate of sexual assault does not even correlate with the rise in consumption of pornography in general.

I think there is a stronger reason to believe that even if there are negative effects from real-life porn, that fictional porn in which reality itself is bent, with immense scapes of fantasy and wonder, grotesque bodies, unreasonable attitudes, twisted scenarios, and strong elements of parody will have less of an effect, or even no effect.