The people have the right to choose what is right for them and for that matter choose whatever that makes them happy. The fact that it might be dangerous to their health doesn't mean one should not have access to it, if he chooses to. These people must have pre-informed decision as to what can happen to them in the near future. So if this person stills goes in for it after the education on the possible implications then he has been informed enough to choose what is good for him and for that matter what makes him happy and is consensus to it. This reason makes is necessary for education.
An education campaign on caffeinated alcohol drinks is better than a complete ban. Bans tend to make people, who would normally be uninterested, suddently interested in a product. A ban would create a black market. It is better to educate people about what they are drinking and to allow them to make the final decision.
I'm not sure who is proposing we ban caffeinated alcohol, but why would we ban that if we weren't banning alcohol already, or weren't banning caffeine already? Ultimately it's up to the drinker to decide what they want to do unless the effects of caffeine and alcohol can be shown to negatively affect others.