i disagree. first, what OP was describing is NOT what i would call food aggression, but rather sounds more like "high value object" possession aggression. a marrow bone filled with peanut butter is pretty high on the list of way-cool-things for dogs. also, this dog is not in his normal environment, or with his normal people. remember that dogs don't generalize- we don't know that his people are just "letting it go"- they may be able to take the highest value item straight out of their dogs mouth, but this dog was in a kennel environment with other dogs, which is a stressful environment, and the OP taking it away was not the dog's person.
in a more general sense, pit bulls are still dogs. high value items are still high value items for pit bulls. even if we SHOULD be able to take things away from all pit bulls in all situations, that's not always feasible or realistic. it may be more realistic to have an understanding and expectations of your dog/pit bull: my dog will growl over raw bones but not rawhide. my dog will not guard kibble, but might guard wet food,etc. if none of the above is acceptable, you should teach your dog waht IS acceptable. if any of the above is acceptable, and your dog may guard his very very special raw b one, you'll probably want to manage that accordingly- not have him have a raw bone when there are visitors, let the kennel where he is boarding know, etc.
just my .02 cents.