Here's the thing. I understand there is a difference between reading Nabokov and looking at child porn. But the fact is, there IS such a thing as obscenity. Pornography, in any form, has a lot of damaging effects on people and on society. There is, right now, a thriving child porn industry that DOESN'T go away. There are children and adults being abused sexually and recorded on film. Now that industry exists because demand exists. I see no reason NOT to examine this material and determine whether it meets the legal definition of obscentiy (scant though that definition is). I know that the libertarian/liberal viewpoint says the government has no business controlling "victimless" behavior, but the issue of pornography (like the drug issue) goes far beyond the actions of consenting adults in "victimless" crimes.
I'm not even going to bother to go into battle on this issue, because I've heard it all before. But the fact is, some things are wrong and ought to be discouraged. There is a responsibility to protect freedom by using it appropriately.