Another possibility, avoiding Hanlon's razor: They honestly have trouble understanding how or why someone could in good conscience disagree. They don't want control or censorship in the abstract; they just want to legislate morality on this one issue because their position is so "obviously" right. Using laws like this to censor things that don't harm kids would be unthinkable, but harming kids is clearly bad, so this law neither is nor opens up the door for censorship. They don't see the slope because the motives look completely different.