Allow me to play Devil's Advocate here.....
It probably should be banned. It's flavor is like candied syrup and is targeted toward younger drinkers. In fact, I'd surmise that it is targeted toward underage drinkers. I tend to feel that any drink whose flavor mimics candy or gatorade or something easily drinkable like that is targeted toward underage drinkers.
Anyone familiar with how businesses selling consumer products runs themselves knows that these companies try to get people buying their product at as young an age as possible. Four Loko knows teenagers are going to get their hands on their product some way, somehow and that teenagers tend to just drink until they hit the floor. So why not design a drink that will enable them to essentially consume more of their product, regardless of how unsafe it may be.
I don't think that govt should protect us from ourselves, but as long as it IS doing this, then products like Four Loko are exactly the types of things they should go after. There's no control with a product like that. First of all, it IS dangerous to drink large quantities of a drink with that much sugar and caffeine AND alcohol in it.
Secondly, while large quantities of alcohol of any kind can be dangerous, it is much more dangerous when combined with large amounts of any stimulant. At a bar, there is always a bartender who can cut you off when you've had too much, but drinking in the privacy of your home leaves no one to moderate for you. This drink is basically designed to drastically lessen your ability to self-regulate yourself while drinking so that you can continue to drink even more. It's not as severe as drinking in conjunction with a bunch of cocaine (and I can tell you from experience that THAT can lead to disaster before you even know what's hit you) but it is the same concept.