I don't agree that dogs understand "stealing" is bad or wrong any more than peeing in the house. They learn they get in trouble, or you teach them where you want them to go. They don't go outside because they think it is wrong to pee on the carpet, they go because you get them into a learned habit to do so. Food guarding is a normal behavior. We teach them not to, or they comprehend we are the food controllers, but I would rather have food aggression than any other type because it IS controllable and trainable.
The leave it command is wonderful, but you need to work on it with a variety of objects, not desirable food, and get it SOLID before food. I also think treating a dog is simply good common dog sense. FOOD they understand, so why not reward good behavior.
You must step back and reteach that food, ALL food, is under your control. K9Deb (Debbi McKean) has a very good article on it:
http://k9deb.com/foodguar.htm
Additionally, Mary's site helps with leave it command. http://www.clickerlessons.com/
You want to deal with things in a way where you do NOT get bitten. If that means you leash the dog while working with food, do so. But I promise you, being food aggressive doesn't mean your dog is bad, unhinged or on the verge of Cujoism. I have worked with dogs who starved on the streets and were highly aggressive about food because, well, they'd have starved otherwise. Even these adult dogs with little relationship to me learned by obedience training, food training, and the leave it command.
I do have to say though, I teach "look at me" even before leave it. (use a shorter word– such as FOCUS or whatever) Usually if you teach a dog to make eye contact, you help break the current obsession (that roll) and give it a moment to focus on you, realize it won't be hurt, be able to comply with the next command.