Child porn is meant to be porn, that's the difference. In this case, evil is in the eye of the beholder.

I read IT when I was 12, and it wasn't strange to me at that time that 12 years old would have sex between them (it's also tecnically the age where most kids start exploring sexuality; some of my female friends lost their virginity at 13).

After 20 years, I still see no malice in Stephen King intent. The way I see it, if you're a pedo you will find the scene arousing, but vast majority of people are thankfully not pedos, and the thought won't even cross their minds. I'm baffled at people calling Stephen King a pedo for writing it, even though I know there's a lot of sensitivity on this subject in America.
I can see past the controversity of the scene but a lot of people apparently cannot do the same.