Correct me if I'm wrong, but I thought that unlawful activity existed outside of the law, anyway.
Meaning, if (for example) I sell you heroin, you can't sue me in small claims court saying that I cut it with baby laxatives and therefore you demand your money back.
If that's how things work, then if Comcast were to block a child porn site, the child porn site couldn't take Comcast to court over it and expect to win. Regardless of any net neutrality laws.