The definitive answer from the cruise line will be to tell you that you can't or shouldn't.
People do it anyway. I have mixed feelings about it. I don't drink, don't like people being told what they can or can't bring with them, but also don't like the prospect of people carting kegs, and tons of beer onto a ship with them.
I suppose the policy is better than no policy at all, lest thing get out of hand, which they surly would.
NWLB - the reason that this policy exists is exactly the reason you mentioned. Not too too many years age the cruise lines would allow you bring aboard liquor, within reason, but people began abusing that policy, trying to bring aboard wheeled coolers full of beer, etc, etc, and the cruise lines cracked down and instituted the liquor policies.
We have brought one of those 24 cartons of soda in our carry on a couple of times with no problems. Sam's Club sells a 36 soda carton that can fit in your carry on. I have no problem paying only 21 cents instead of $1.75 for a soda.
Teresa and Larry
#36-Carnival Splendor 9/16/12
7 night Mexican Riviera
#37-Allure of the Seas 11/11/12
7 night Eastern Caribbean
We're heading out in 3 weeks for my first cruise, husband's 4th. The booking agent (Not RCI) said a lot of people put cases of soda or a bottle in their luggage. I will probably do the same. We're in our 40s and are not wild, crazy, drunks - but we do like to have a cocktail before dinner, and a nightcap on the balcony before sleep.
Certainly people shouldn't roll kegs or coolers on board, but if you're responsible, I don't what the big deal is. We do it at hotels and resorts all the time.
NWLB - the cruise line will usually let you bring aboard a REASONABLE amount of soda- brands or types that they do not sell onboard with not much hassle. Buy a six-pack at your port of departure,put it in you carry-on and then replenish your supply from the grocery stores on each island.
My husband and I have traveled on RCCL 10 times and we have always brought some of our own liquor. We usually bring two large bottles and wrap them in clothing and secure them in our luggage. We still end up purchasing liquor on board including wine. But, it is still nice to have something in your state room. I know this is suppose to be a no-no, but we still do it!!