My interpretation of laws are limitations on people's freedom that are imposed to protect the "natural" or "inalienable" rights of others. A secondary (and controversial, although both American liberals and conservatives both use and decry it for their own purposes) feature is to use it for the benefit of the entire society (utilitarianism). So an example of the former would be property rights, and an example of the latter would be bans on trans fat.
My take on lolicon bans is this. It causes really damage (imprisonment, fines, humiliation, etc) for no benefit whatsoever to society or to individuals.
Let's analyze bans on child pornography though. I like the logic to ban it, not based on obscenity, but because it harms the rights of individuals (the children involved in the making of the product). Obviously the making of the material involves harming the child, and the circulation of the material goes against the child's will and further humiliates them.
The circulation of the material and ownership of the material should be stopped, not just based on the issue of consent and humiliation, but because it will cripple the MARKET that exists for such material. Crippling the market, will greatly decrease the supply and demand for the product (yes, demand too. If you increase the risk of being caught and arrested, that adds a cost to each purchase).
Now let's look at lolicon. There's no individual harmed in the process of making the material. None. Therefore, there's no reason to ban the creation of it, as well as the ownership and circulation of it as well. There's no need to attack the supply and demand of it, since there's no harm with the market existing.
The only possible argument that exists, the one that all anti-videogame/movie/music/etc proponents fall back to is that such material increases risk for dangerous behavior (this falls into the secondary usage of laws: utilitarianism). But there is not an overwhelmingly strong evidence for such a thing. It's not a scientifically proven fact yet. We shouldn't base any law, or limit the rights of individuals based on unproven things. A few dubious studies (if there are any) aren't enough.
