

About aspartame, there is no real proof out there, only warnings. Also, to cause bad effects to your body like cancers, the doses you'd have to take would be extremely high, more than what one would eat in one's life. And so everybody knows, many things contain aspartame, like most of the chewing gums.
Caffeine is really bad for many reasons, and should be avoided. The recommendations out there say that a person should not drink more than one cup of coffee per day, and some studies even say less. Add other caffeine products and you're done

Also, some people don't realize the effect of plain sugar. Even if you don't eat much fats, sugar in too big quantities can be converted and stored like fats. Like somebody already pointed out, it can also lead to some forms of diabetes and well, bring all the risks that comes with more adipose tissue in your body.
I guess seeing the bads effects with my own eyes has helped a lot to consider what I'm eating/drinking. That's why I think the movie "Supersize Me" is actually a very good way to help people see the facts better.