This would outlaw advertising that is effective then, since the entire goal of an advertisement is to maximize the difference between A and B. So to do any advertising you'd have to prove it wasn't very effective? Sounds similar to types of proposed gun regulation: "your guns can kill people, just not too many too fast too effectively"

Not that that means it's necessarily a bad approach, just never heard of marketing being limited by its effectiveness. Similar to having to put those gross pictures on cigarette packages now.