Aspartame has not ben proven to be bad for people and probably isnt as bad as sugar.
I love how people throw around the word "Carcinogen" today.
Of 62 known carcinogens 12 are naturally occouring in the human diet. Estrogen for example is a carcinogen we all have and most of us at unsafe levels.
Is aspartame bad? We don't know. Its not cyanide though which is in many things we eat as well. Perfectly safe in small doses.

Chugging redbull is not natural.
Anything used in excess will have effects.
Effects in some will be worse than in others.

Moderation.