Child fucking is outlawed because it physically harms the child and the child can't consent. Obsessing to fuck the child can eventually lead one to act on fucking a child which is why places ban child porn and even cartoons or hell parents owning naked pics of their own kids depending how extreme.
Some pedos are gay but not gays are pedos. Just like some hetros are pedos but not all pedos are hetro. If you want to explain why we should all breathe a sigh of relief that a 30 year old man only targets 7 year old girls instead of 7 year old boys be my guest.