In between what the law bans and what the law permits, there's all the "you're allowed to do it because nobody said you can't" stuff. If you happen to be doing that stuff, it's comforting to have it explicitly called out as legal. If you want that stuff to be illegal, you obviously don't want it getting promoted to "more" legal, because it's harder to get your ban passed.

Imagine a new bill is introduced. "Eating apples is legal." The Apple Pickers Union would love to see this bill passed. The Orange Pickers Union would probably oppose it. They'd both spend millions on a blogocampaign to convince you they are right. But passing (or not passing) the bill changes nothing; it's already legal to eat apples.